Damping valve and shock absorber

ABSTRACT

A damping valve includes a valve disc including a passage and a valve seat configured to surround an outlet end of the passage, a leaf valve configured to separate from/sit on the valve seat to open/close the passage, and a biasing part configured to exert a variable biasing force on the leaf valve toward the valve disc, and a gap is provided between the leaf valve and the valve seat.

This is a Division of U.S. application Ser. No. 15/528,809, filed on May23, 2017, which was a National Stage application of PCT/JP2015/082927,filed Nov. 24, 2015, the subject matters of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a damping valve and a shock absorber.

BACKGROUND ART

A shock absorber used in a vehicle suspension is equipped with a dampingvalve that can vary a damping force. Such a shock absorber includes: acylinder; a piston that partitions the inside of the cylinder into anextension-side chamber and a contraction-side chamber; a piston rodconnected to the piston at one end and movably inserted into thecylinder; and a damping valve. The damping valve includes: a passageprovided to the piston; a disc valve that separates from and sits on anannular valve seat that surrounds an outlet end of the passage providedto the piston; a back pressure chamber that causes pressure led from theextension-side chamber or the contraction-side chamber to act on theback surface of the disc valve; and a solenoid pressure control valvethat controls the pressure within the back pressure chamber. The passageof the piston allows the extension-side chamber to communicate with thecontraction-side chamber. The disc valve opens/closes the passage byseparating from or sitting on the valve seat. A solenoid is used in thesolenoid pressure control valve (for example, refer to JP2001-12530A).

In such a shock absorber, the damping force during extension and duringcontraction is controlled by controlling the pressure within the backpressure chamber using the solenoid pressure control valve. In aclosed-valve state in which the disc valve is seated on the valve seat,liquid within the cylinder passes through a fixed orifice provided tothe disc valve and enters/exits the extension-side chamber and thecontraction-side chamber. When the piston moves at a low speed, theshock absorber mainly exerts the damping force with the fixed orifice.

SUMMARY OF INVENTION

In a vehicle shock absorber, there are cases in which the damping forceneeds to be decreased when the piston speed is in a low-speed region forthe purpose of improving the riding comfort in the vehicle. Inconventional shock absorbers, the damping force is exerted with thefixed orifice until an opened-valve state is reached in which the discvalve separates from the valve seat. Therein, in order to decrease thedamping force, it is necessary to increase the opening area of the fixedorifice. When the opening area of the fixed orifice is increased, thedamping force can be reliably decreased, but the maximum value of thedamping force is determined by the fixed orifice. Thus, the dampingforce adjustment width is remarkably reduced.

When the disc valve is not provided with an orifice, the damping forceadjustment width increases. However, even if the damping forcecharacteristics of the shock absorber are set to full soft, the dampingforce may increase too much and this may worsen the riding comfort inthe vehicle.

An object of the present invention is to provide a damping valve and ashock absorber with which the damping force when the piston speed is ina low-speed region can be decreased and the damping force adjustmentwidth can be expanded.

According to one aspect of the present invention, a damping valveincludes a valve disc including a passage and a valve seat configured tosurround an outlet end of the passage, a leaf valve configured toseparate from/sit on the valve seat to open/close the passage, and abiasing part configured to exert a variable biasing force on the leafvalve toward the valve disc, and a gap is provided between the leafvalve and the valve seat.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-section view of a shock absorber using a damping valveaccording to a first embodiment of the present invention;

FIG. 2 is a partially enlarged cross-section view of the shock absorberusing the damping valve according to the first embodiment of the presentinvention;

FIG. 3 is an enlarged cross-section view of the damping valve accordingto the first embodiment of the present invention;

FIG. 4 is a diagram for explaining the damping force characteristics ofthe shock absorber using the damping valve according to the firstembodiment of the present invention;

FIG. 5 is a cross-section view of a shock absorber using a damping valveaccording to a second embodiment of the present invention;

FIG. 6 is a partially enlarged cross-section view of the shock absorberusing the damping valve according to the second embodiment of thepresent invention;

FIG. 7 is an enlarged cross-section view of the damping valve accordingto the second embodiment of the present invention; and

FIG. 8 is a diagram for explaining the damping force characteristics ofthe shock absorber using the damping valve according to the secondembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention will now be explained based on the illustratedembodiments.

First Embodiment

As shown in FIG. 1 , a damping valve according to a first embodiment isutilized as both an extension-side damping valve and a contraction-sidedamping valve of a shock absorber D1. The damping valve includes thefollowing: a piston 2 serving as a valve disc; an annular extension-sideleaf valve Ve; an annular contraction-side leaf valve Vp; and a biasingpart that exerts a variable biasing force on the extension-side leafvalve toward the piston 2 side and exerts a variable biasing force onthe contraction-side leaf valve toward the piston 2 side. The piston 2includes an extension-side passage 3 and a contraction-side passage 4which serve as a passage, and an annular extension-side valve seat 2 dand an annular contraction-side valve seat 2 c that respectivelysurround the outlet ends of the extension-side passage 3 and thecontraction-side passage 4. The extension-side leaf valve Ve separatesfrom and sits on the extension-side valve seat 2 d to open and close theextension-side passage 3. The contraction-side leaf valve Vp separatesfrom and sits on the contraction-side valve seat 2 c to open and closethe contraction-side passage 4. The extension-side leaf valve Ve and thecontraction-side leaf valve Vp are laminated on the piston 2. Thebiasing part exerts a variable biasing force on the extension-side leafvalve Ve toward the piston 2 side and exerts a variable biasing force onthe contraction-side leaf valve Vp toward the piston 2 side. The dampingvalve of the present embodiment obviously may be applied to only theextension-side damping valve or to only the contraction-side dampingvalve of the shock absorber D1.

Meanwhile, the shock absorber D1 includes the following: a cylinder 1that is filled with a liquid such as a hydraulic oil; the damping valvethat is accommodated within the cylinder 1; an extension-side chamber R1and a contraction-side chamber R2 that are partitioned within thecylinder 1 by the piston 2 which serves as a valve disc that constitutesthe damping valve; and a piston rod 7 that is movably inserted into thecylinder 1 and connected to the piston 2. The piston 2 is inserted intothe cylinder 1 such that the piston 2 can move in the axial direction.When the piston 2 moves in the axial direction (the up-down direction inFIG. 1 ) relative to the cylinder 1, the shock absorber D1 appliesresistance with the extension-side leaf valve Ve to the flow of liquidpassing through the extension-side passage 3, and applies resistancewith the contraction-side leaf valve Vp to the flow of liquid passingthrough the contraction-side passage 4, and thereby exerts a dampingforce.

Although not illustrated, a free piston that slides through the insideof the cylinder 1 is provided at the bottom in FIG. 1 of the cylinder 1.A gas chamber is formed within the cylinder 1 by the free piston. Thepiston 2 is connected to one end of the piston rod 7 that is movablyinserted into the cylinder 1. The piston rod 7 penetrates through theinner periphery of an annular rod guide (not illustrated) that isprovided at the top end of the cylinder 1, and protrudes to the outsideof the cylinder 1. A seal (not illustrated) is provided between thepiston rod 7 and the cylinder 1, and the inside of the cylinder 1 is ina liquid-tight state due to this seal. As illustrated, the shockabsorber D1 is set to a so-called single-rod type. The volume of thepiston rod 7 that moves into/out of the cylinder 1 according to theextension/contraction of the shock absorber D1 is compensated by meansof the volume of the gas within the gas chamber expanding or contractingand the free piston moving through the inside of the cylinder 1 in theup-down direction. In this way, the shock absorber D1 is set to asingle-cylinder type. However, instead of installing the free piston andthe gas chamber, a reservoir may be provided on the outer periphery oroutside of the cylinder 1 and volume compensation of the piston rod 7may be performed by this reservoir.

In this embodiment, the biasing part of the damping valve includes thefollowing: an extension-side spool Se that biases the extension-sideleaf valve Ve; an extension-side back pressure chamber Ce that pressesthe extension-side spool Se with internal pressure; a contraction-sidespool Sp that biases the contraction-side leaf valve Vp; acontraction-side back pressure chamber Cp that presses thecontraction-side spool Sp with internal pressure; a communicationpassage 24 that communicates with the contraction-side back pressurechamber Cp via an extension-side pilot orifice Pe serving as anextension-side resistance element, and that communicates with theextension-side back pressure chamber Ce via a contraction-side pilotorifice Pp serving as a contraction-side resistance element; anextension-side pressure introduction passage Ie that permits only theflow of liquid from the extension-side chamber R1 toward thecontraction-side back pressure chamber Cp; a contraction-side pressureintroduction passage Ip that permits only the flow of liquid from thecontraction-side chamber R2 toward the extension-side back pressurechamber Ce; an adjustment passage Pc that is connected to thecommunication passage 24; a contraction-side discharge passage Ep thatallows the downstream of the adjustment passage Pc to communicate withthe extension-side chamber R1, and that permits only the flow of liquidfrom the adjustment passage Pc toward the extension-side chamber R1; anextension-side discharge passage Ee that allows the downstream of theadjustment passage Pc to communicate with the contraction-side chamberR2, and that permits only the flow of liquid from the adjustment passagePc toward the contraction-side chamber R2; and a solenoid pressurecontrol valve 6 provided in the adjustment passage Pc. Theextension-side pilot orifice Pe applies resistance to the flow of liquidpassing through the extension-side pilot orifice Pe. Thecontraction-side pilot orifice Pp applies resistance to the flow ofliquid passing through the contraction-side pilot orifice Pp. Thesolenoid pressure control valve 6 controls the upstream pressure of theadjustment passage Pc.

The damping valve and the shock absorber D1 will now be explained indetail below. In the first embodiment, the piston rod 7 is formed by thefollowing: a piston retaining member 8 that retains the piston 2; asolenoid valve accommodation tube 9 that is connected at one end to thepiston retaining member 8; and a rod member 10 that is connected at oneend to the solenoid valve accommodation tube 9 and protrudes at theother end to the outside from the top end of the cylinder 1. Thesolenoid valve accommodation tube 9 forms, together with the pistonretaining member 8, a hollow accommodation part L that accommodates thesolenoid pressure control valve 6.

The piston retaining member 8 includes: a retaining shaft 8 a, theannular piston 2 being mounted on the outer periphery thereof; a flange8 b provided on the outer periphery at the top end in FIG. 1 of theretaining shaft 8 a; and a cylindrical socket 8 c provided on the outerperiphery at the top end in FIG. 1 of the flange 8 b. The pistonretaining member 8 also includes the following: a vertical hole 8 d thatopens from the top end of the retaining shaft 8 a and extends in theaxial direction; an annular groove 8 e provided to the bottom end inFIG. 1 of the flange 8 b so as to surround the retaining shaft 8 a; aport 8 f that allows the annular groove 8 e to communicate with theinside of the socket 8 c; a horizontal hole 8 g that allows the annulargroove 8 e to communicate with the inside of the vertical hole 8 d; theextension-side pilot orifice Pe serving as an extension-side resistanceelement; the contraction-side pilot orifice Pp serving as acontraction-side resistance element; a threaded part 8 i provided on theouter periphery at the bottom end in FIG. 1 of the retaining shaft 8 a;and a groove 8 j formed on the top end of the flange 8 b. The verticalhole 8 d communicates with the inside of the socket 8 c. Theextension-side pilot orifice Pe and the contraction-side pilot orificePp open from the outer periphery of the retaining shaft 8 a tocommunicate with the vertical hole 8 d. The groove 8 j communicates withthe vertical hole 8 d.

A cylindrical separator 23 is inserted into the vertical hole 8 dprovided to the retaining shaft 8 a. An annular groove 23 a is providedon the outer periphery of the separator 23. The separator 23 forms, withthe annular groove 23 a, the communication passage 24 that allows theextension-side pilot orifice Pe to communicate with the contraction-sidepilot orifice Pp within the vertical hole 8 d. An annular valve seat 23b that surrounds the opening at the bottom end in FIG. 1 of theseparator 23 is provided to the bottom end of the separator 23. Thevertical hole 8 d allows the contraction-side chamber R2 to communicatewith the inside of the socket 8 c via the separator 23. On the otherhand, the separator 23 is formed so that the extension-side pilotorifice Pe and the contraction-side pilot orifice Pp do not communicatevia the vertical hole 8 d with the contraction-side chamber R2 and theinside of the socket 8 c. Further, the horizontal hole 8 g alsocommunicates with the communication passage 24. The separator 23 isformed so that the horizontal hole 8 g does not communicate via theinside of the vertical hole 8 d with the contraction-side chamber R2 andthe inside of the socket 8 c.

The extension-side resistance element and the contraction-sideresistance element are sufficient as long as they apply resistance tothe flow of liquid passing therethrough, and thus they are not limitedto orifices. For example, the extension-side resistance element and thecontraction-side resistance element may be configured as otherrestrictors such as choke passages, and may also be configured as valvesthat apply resistance such as leaf valves or poppet valves.

An annular recess 8 k is provided on the outer periphery at the top endin FIG. 1 of the socket 8 c. A through hole 8 m that communicates withthe inside of the socket 8 c from the recess 8 k is provided in thesocket 8 c. An annular plate 22 a is mounted in the recess 8 k. Theannular plate 22 a is biased from above in FIG. 1 by a spring member 22b so as to close the through hole 8 m.

The solenoid valve accommodation tube 9 includes: a closed-topcylindrical accommodation tube part 9 a; a cylindrical connection part 9b that extends upwards in FIG. 1 from the top part of the accommodationtube part 9 a; and a through hole 9 c that opens from the side of theaccommodation tube part 9 a and communicates with the inside thereof.The outer diameter of the connection part 9 b is smaller than the outerdiameter of the accommodation tube part 9 a. The piston retaining member8 is integrated with the solenoid valve accommodation tube 9 by screwingthe socket 8 c of the piston retaining member 8 into the inner peripheryof the accommodation tube part 9 a of the solenoid valve accommodationtube 9. By this screwing, the accommodation part L that accommodates thesolenoid pressure control valve 6 is formed within the accommodationtube part 9 a by the solenoid valve accommodation tube 9 and the pistonretaining member 8. A portion of the adjustment passage Pc (to beexplained in detail later) is provided within the accommodation part L.The accommodation part L is in communication with the communicationpassage 24 by means of the port 8 f, the annular groove 8 e, and thehorizontal hole 8 g explained above. A portion of the adjustment passagePc is formed by the port 8 f, the annular groove 8 e, and the horizontalhole 8 g. As long as the accommodation part L is in communication withthe communication passage 24, the port 8 f, the annular groove 8 e, andthe horizontal hole 8 g do not have to be used, and a passage thatdirectly allows the accommodation part L to communicate with thecommunication passage 24 may be provided. Using the port 8 f, theannular groove 8 e, and the horizontal hole 8 g is advantageous becausethe machining of the passage for allowing the accommodation part L tocommunicate with the communication passage 24 becomes easier.

When the piston retaining member 8 is integrated with the solenoid valveaccommodation tube 9, the through hole 9 c opposes the recess 8 k. Thethrough hole 9 c allows the accommodation part L to communicate with theextension-side chamber R1 in cooperation with the through hole 8 m. Acheck valve 22 that permits only the flow of liquid from within theaccommodation part L toward the extension-side chamber R1 is formed bythe annular plate 22 a and the spring member 22 b. In other words, thecontraction-side discharge passage Ep is formed by the through hole 9 c,the recess 8 k, the through hole 8 m, and the check valve 22.

A check valve 25, which separates from and sits on the annular valveseat 23 b provided to the bottom end in FIG. 1 of the separator 23, isprovided within the vertical hole 8 d of the piston retaining member 8.The check valve 25 stops the flow of liquid from the contraction-sidechamber R2 side toward the accommodation part L, and permits only theflow of liquid from the accommodation part L toward the contraction-sidechamber R2. In other words, the extension-side discharge passage Ee isformed within the vertical hole 8 d by the separator 23.

The rod member 10 has a cylindrical shape. The inner periphery at thebottom end in FIG. 1 of the rod member 10 is expanded in diameter so asto permit the insertion of the connection part 9 b of the solenoid valveaccommodation tube 9. The rod member 10 has on its inner periphery athreaded part (not assigned a reference numeral) that enables thescrewing of the connection part 9 b. The piston rod 7 is formed byintegrating the rod member 10, the solenoid valve accommodation tube 9,and the piston retaining member 8.

A harness H which supplies power to a solenoid (to be explained later)is inserted into the rod member 10 and into the connection part 9 b ofthe solenoid valve accommodation tube 9. Although not illustrated, thetop end of the harness H extends outward from the top end of the rodmember 10 and is connected to a power source.

As shown in FIG. 3 , the annular piston 2 is assembled onto the outerperiphery of the retaining shaft 8 a provided to the piston retainingmember 8. The following are assembled onto the outer periphery of theretaining shaft 8 a above the piston 2 in FIG. 3 : a contraction-sideannular spacer 60 serving as an annular spacer; the contraction-sideleaf valve Vp; a contraction-side spacer 61 serving as a spacer; acontraction-side annular plate 62 serving as an annular plate; acontraction-side plate stopper 63; the contraction-side spool Sp; and acontraction-side chamber 11. The contraction-side chamber 11 forms thecontraction-side back pressure chamber Cp. The following are assembledonto the outer periphery of the retaining shaft 8 a under the piston 2in FIG. 3 : an extension-side annular spacer 64 serving as an annularspacer; the extension-side leaf valve Ve; an extension-side spacer 65serving as a spacer; an extension-side annular plate 66 serving as anannular plate; an extension-side plate stopper 67; the extension-sidespool Se; and an extension-side chamber 12. The extension-side chamber12 forms the extension-side back pressure chamber Ce.

The piston 2 is formed by stacking discs 2 a, 2 b so that the piston 2is divided into a top half and a bottom half. The extension-side passage3 and the contraction-side passage 4, each of which allows theextension-side chamber R1 to communicate with the contraction-sidechamber R2, are formed in the piston 2. In this way, by forming thepiston 2 with the discs 2 a, 2 b so that the piston 2 is divided intotop and bottom halves, the extension-side passage 3 and thecontraction-side passage 4, which have complex shapes, can be formedwithout requiring any drilling processing, and thus the piston 2 can bemanufactured easily and inexpensively. Further, the disc 2 a on the topside in FIG. 3 includes: an annular window 2 e provided on the top endthereof; the annular contraction-side valve seat 2 c provided on theouter periphery side of the annular window 2 e; and an inner peripheralseat part 2 f provided on the inner periphery of the annular window 2 e.The annular window 2 e is in communication with the contraction-sidepassage 4. The contraction-side valve seat 2 c surrounds thecontraction-side passage 4. On the other hand, the disc 2 b on thebottom side includes: an annular window 2 g provided on the bottom endthereof; the annular extension-side valve seat 2 d provided on the outerperiphery side of the annular window 2 g; and an inner peripheral seatpart 2 h provided on the inner periphery of the annular window 2 g. Theannular window 2 g is in communication with the extension-side passage3. The extension-side valve seat 2 d surrounds the extension-sidepassage 3.

As shown in FIG. 3 , the extension-side leaf valve Ve is formed in anannular shape so as to permit the insertion of the retaining shaft 8 aof the piston retaining member 8. In this embodiment, the extension-sideleaf valve Ve is constituted by stacking two annular plates 71 and 72 oneach other. The inner periphery of the extension-side leaf valve Ve issandwiched by the piston 2 and the extension-side chamber 12, and due tothis sandwiching, the extension-side leaf valve Ve is fixed to theretaining shaft 8 a of the piston retaining member 8. Deflection of theouter periphery of the extension-side leaf valve Ve is permitted. Inmore detail, the extension-side spacer 65 is interposed between theextension-side leaf valve Ve and the extension-side chamber 12.Deflection of the extension-side leaf valve Ve toward the bottom side inFIG. 3 is permitted more toward the outer periphery side from an areathat is supported by the extension-side spacer 65. Deflection of theextension-side leaf valve Ve toward the top side in FIG. 3 is permittedmore toward an outer periphery side from an area that is supported bythe extension-side annular spacer 64. A notch 71 a that functions as anorifice when seated on the extension-side valve seat 2 d is provided onthe outer periphery of the annular plate 71 disposed on the piston 2side.

The extension-side leaf valve Ve is laminated on the bottom in FIG. 3 ofthe piston 2 via the extension-side annular spacer 64, which islaminated on the inner peripheral seat part 2 h of the piston 2. In astate in which a load is not acting on the extension-side leaf valve Ve,a gap is formed between the extension-side leaf valve Ve and theextension-side valve seat 2 d. The length of this gap in the up-downdirection in FIG. 3 can be adjusted by exchanging for an extension-sideannular spacer 64 of a different thickness or by changing the number ofextension-side annular spacers 64 that are laminated. The gap betweenthe extension-side leaf valve Ve and the extension-side valve seat 2 dcan be formed without using the extension-side annular spacer 64 bysetting the height of the inner peripheral seat part 2 h to be greaterthan the height of the extension-side valve seat 2 d and directlylaminating the extension-side leaf valve Ve onto the inner peripheralseat part 2 h. However, by providing the extension-side annular spacer64 to the inner peripheral seat part 2 h, the above-mentioned length ofthe gap can be easily adjusted.

The extension-side leaf valve Ve deflects when a biasing force is loadedthereon by the biasing part from the back surface side (opposite side ofthe piston 2). If this biasing force increases, the extension-side leafvalve Ve sits onto the extension-side valve seat 2 d so as to close theextension-side passage 3. In this state, the extension-side passage 3communicates with the contraction-side chamber R2 via only the notch 71a.

The extension-side annular plate 66 is slidably mounted on the outerperiphery of the extension-side spacer 65. The axial direction length ofthe extension-side annular plate 66 is shorter than the axial directionlength of the extension-side spacer 65. Thus, the extension-side annularplate 66 can move in the up-down direction while slidingly contactingthe outer periphery of the extension-side spacer 65. Further, theannular extension-side plate stopper 67 is provided to the bottom inFIG. 3 of the extension-side spacer 65. The outer diameter of theextension-side plate stopper 67 is set to be greater than the innerdiameter of the extension-side annular plate 66. The extension-sidechamber 12 is laminated on the bottom of the extension-side platestopper 67. The inner diameter of the extension-side annular plate 66 isset to be smaller than the outer diameter of the inner peripheral seatpart 2 h provided to the piston 2. The outer diameter of theextension-side annular plate 66 is set to be greater than the innerdiameter of the extension-side valve seat 2 d. The extension-sideannular plate 66 is configured such that it can move in the axialdirection (the up-down direction in FIG. 3 ) between the extension-sideannular spacer 64 and the extension-side plate stopper 67.

The extension-side annular plate 66 has a higher deflection rigiditythan that of the annular plates 71, 72 that constitute theextension-side leaf valve Ve. In the present embodiment, by setting theaxial direction length (thickness) of the extension-side annular plate66 to be greater than the axial direction length (thickness) of theannular plates 71, 72 of the extension-side leaf valve Ve, the rigidityof the extension-side annular plate 66 can be increased to be greaterthan the rigidity of the extension-side leaf valve Ve. Not only can therigidity be strengthened by the thickness, but the rigidity of theextension-side annular plate 66 can also be increased by forming theextension-side annular plate 66 with a material having a higher rigiditythan that of the extension-side leaf valve Ve.

When the extension-side annular plate 66 is compressed from the backsurface side by the pressure within the extension-side back pressurechamber Ce and the extension-side spool Se, the extension-side annularplate 66 pushes up the extension-side leaf valve Ve causing it todeflect. When the extension-side leaf valve Ve deflects to the point atwhich it sits on the extension-side valve seat 2 d, the extension-sideannular plate 66 enters a state in which it is supported by the innerperipheral seat part 2 h and the extension-side valve seat 2 d. In thisstate, the biasing force generated by the pressure within theextension-side back pressure chamber Ce and the extension-side spool Seis received by the extension-side annular plate 66. Thus, any furtherdeformation of the extension-side leaf valve Ve is suppressed, and anexcessive load is prevented from being applied to the extension-sideleaf valve Ve. Further, the extension-side annular plate 66 is slidablymounted on the extension-side spacer 65. Therefore, when theextension-side leaf valve Ve deflects in a direction away from theextension-side valve seat 2 d, the extension-side annular plate 66 movesdownward in FIG. 3 relative to the extension-side spacer 65. Thus, thedeflection of the extension-side leaf valve Ve in the direction awayfrom the piston 2 is not obstructed by the extension-side annular plate66.

The extension-side chamber 12 includes: a tubular mounting part 12 athat is fitted onto the outer periphery of the retaining shaft 8 a ofthe piston retaining member 8; a flange 12 b that is provided on theouter periphery at the bottom end in FIG. 3 of the mounting part 12 a; asliding contact tube 12 c that extends from the outer periphery of theflange 12 b toward the piston 2 side; an annular groove 12 d provided onthe inner periphery of the mounting part 12 a; and a notch 12 e thatcommunicates with the annular groove 12 d from the outer periphery ofthe mounting part 12 a. In a state in which the extension-side chamber12 is assembled onto the retaining shaft 8 a, the annular groove 12 dopposes the contraction-side pilot orifice Pp provided to the retainingshaft 8 a. The extension-side plate stopper 67 is interposed between themounting part 12 a of the extension-side chamber 12 and theextension-side spacer 65. The extension-side plate stopper 67 may beeliminated and the lower limit of movement of the extension-side annularplate 66 may be restricted with the mounting part 12 a. There are casesin which it is necessary to adjust the position of the extension-sidechamber 12 so that it opposes the contraction-side pilot orifice Pp andthe annular groove 12 d when assembling the extension-side chamber 12onto the retaining shaft 8 a of the piston retaining member 8, and insuch cases, the extension-side plate stopper 67 is preferably providedbetween the mounting part 12 a and the extension-side spacer 65. Theposition of the extension-side chamber 12 relative to the pistonretaining member 8 can be adjusted by the extension-side plate stopper67.

The extension-side spool Se is accommodated within the sliding contacttube 12 c. The outer periphery of the extension-side spool Se slidinglycontacts the inner periphery of the sliding contact tube 12 c, and theextension-side spool Se is configured such that it can move in the axialdirection within the sliding contact tube 12 c. The extension-side spoolSe has an annular spool main body 13, and an annular projection 14 thatrises up from the inner periphery at the top end in FIG. 3 of the spoolmain body 13. The inner diameter of the annular projection 14 is set tobe smaller than the outer diameter of the extension-side annular plate66, and the annular projection 14 is configured such that it can abutthe back surface (bottom surface in FIG. 3 ) of the extension-sideannular plate 66.

When the extension-side spool Se is assembled to the extension-sidechamber 12 and the extension-side chamber 12 is assembled onto theretaining shaft 8 a, the extension-side back pressure chamber Ce isformed on the back surface side (the bottom side in FIG. 3 ) of theextension-side leaf valve Ve. The inner diameter of the spool main body13 is greater than the outer diameter of the mounting part 12 a. Theinner diameter of the spool main body 13 can be set so that the innerperiphery of the spool main body 13 slidingly contacts the outerperiphery of the mounting part 12 a, and the extension-side backpressure chamber Ce can be sealed by the extension-side spool Se.

The annular groove 12 d is provided on the inner periphery of themounting part 12 a of the extension-side chamber 12. The mounting part12 a includes the notch 12 e that communicates with the annular groove12 d from the outer periphery of the mounting part 12 a. In a state inwhich the extension-side chamber 12 is assembled onto the retainingshaft 8 a, the annular groove 12 d opposes the contraction-side pilotorifice Pp provided to the retaining shaft 8 a, and the extension-sideback pressure chamber Ce communicates with the contraction-side pilotorifice Pp.

Further, the contraction-side pressure introduction passage Ip thatopens from the outer periphery of the flange 12 b is provided to theextension-side chamber 12. The contraction-side chamber R2 communicateswith the inside of the extension-side back pressure chamber Ce via thecontraction-side pressure introduction passage Ip. An annular plate 15is laminated on the top end in FIG. 3 of the flange 12 b of theextension-side chamber 12. A spring member 16 is interposed between theannular plate 15 and the spool main body 13 of the extension-side spoolSe. The annular plate 15 is pressed toward the flange 12 b by the springmember 16 so that the contraction-side pressure introduction passage Ipis closed. The contraction-side pressure introduction passage Ip isconfigured so as to not generate any resistance against the flow ofpassing liquid.

If the shock absorber D1 contracts so that the contraction-side chamberR2 is compressed and the pressure therein increases, the annular plate15 is pressed by this pressure so that it separates from the flange 12b, and thereby the contraction-side pressure introduction passage Ip isopened. During extension of the shock absorber D1 in which the pressurewithin the extension-side back pressure chamber Ce increases higher thanthat of the contraction-side chamber R2, the annular plate 15 is pressedto the flange 12 b so as to close the contraction-side pressureintroduction passage Ip. In other words, the annular plate 15 functionsas a valve body of a contraction-side check valve Tp that permits onlythe flow of liquid from the contraction-side chamber R2. By thiscontraction-side check valve Tp, the contraction-side pressureintroduction passage Ip is set to a one-way passage that permits onlythe flow of liquid from the contraction-side chamber R2 toward theextension-side back pressure chamber Ce.

The spring member 16 functions to press the annular plate 15 to theflange 12 b. In other words, the spring member 16 constitutes thecontraction-side check valve Tp together with the valve body (theannular plate 15) of the check valve. The spring member 16 alsofunctions to bias the extension-side spool Se toward the extension-sideleaf valve Ve. When the extension-side leaf valve Ve deflects so thatthe extension-side spool Se is pushed down in the direction away fromthe piston 2 (downwards in FIG. 3 ) and then the deflection of theextension-side leaf valve Ve subsequently terminates, the extension-sidespool Se is still biased by the spring member 16, and thus theextension-side spool Se can quickly return to its original position (theposition shown in FIG. 3 ) following the extension-side leaf valve Ve.It is also possible to bias the extension-side spool Se with a differentspring member from the spring member 16. Using the same spring memberfor the spring member that constitutes the contraction-side check valveTp and the spring member that biases the extension-side spool Se isadvantageous because the number of parts can be reduced and thestructure can be simplified. The outer diameter of the extension-sidespool Se is set to be greater than the inner diameter of the annularprojection 14, and the annular projection 14 is configured to abut theextension-side annular plate 66. The extension-side spool Se isconstantly biased toward the extension-side leaf valve Ve by thepressure of the extension-side back pressure chamber Ce.

As shown in FIG. 3 , similar to the extension-side leaf valve Ve, thecontraction-side leaf valve Vp that is laminated on top of the piston 2is formed in an annular shape so as to permit the insertion of theretaining shaft 8 a of the piston retaining member 8. In thisembodiment, the contraction-side leaf valve Vp is constituted bystacking two annular plates 81 and 82 on each other. The inner peripheryof the contraction-side leaf valve Vp is sandwiched by the piston 2 andthe contraction-side chamber 11, and due to this sandwiching, thecontraction-side leaf valve Vp is fixed to the retaining shaft 8 a ofthe piston retaining member 8. Deflection of the outer periphery of thecontraction-side leaf valve Vp is permitted. In more detail, thecontraction-side spacer 61 is interposed between the contraction-sideleaf valve Vp and the contraction-side chamber 11. Deflection of thecontraction-side leaf valve Vp toward the top side in FIG. 3 ispermitted more toward the outer periphery side from an area that issupported by the contraction-side spacer 61. Deflection of thecontraction-side leaf valve Vp toward the bottom side in FIG. 3 ispermitted more toward an outer periphery side from an area that issupported by the contraction-side annular spacer 60. A notch 81 a thatfunctions as an orifice when seated on the contraction-side valve seat 2c is provided on the outer periphery of the annular plate 81 disposed onthe piston 2 side.

The contraction-side leaf valve Vp is laminated on the top in FIG. 3 ofthe piston 2 via the contraction-side annular spacer 60, which islaminated on the inner peripheral seat part 2 f of the piston 2. In astate in which a load is not acting on the contraction-side leaf valveVp, a gap is formed between the contraction-side leaf valve Vp and thecontraction-side valve seat 2 c. The length of this gap in the up-downdirection in FIG. 3 can be adjusted by exchanging for a contraction-sideannular spacer 60 of a different thickness or by changing the number ofcontraction-side annular spacers 60 that are laminated. The gap betweenthe contraction-side leaf valve Vp and the contraction-side valve seat 2c can be formed without using the contraction-side annular spacer 60 bysetting the height of the inner peripheral seat part 2 f to be greaterthan the height of the contraction-side valve seat 2 c and directlylaminating the contraction-side leaf valve Vp onto the inner peripheralseat part 2 f. However, by providing the contraction-side annular spacer60 to the inner peripheral seat part 2 f, the above-mentioned length ofthe gap can be easily adjusted.

The contraction-side leaf valve Vp deflects when a biasing force isloaded thereon by the biasing part from the back surface side (oppositeside of the piston 2). If this biasing force increases, thecontraction-side leaf valve Vp sits onto the contraction-side valve seat2 c so as to close the contraction-side passage 4. In this state, thecontraction-side passage 4 communicates with the extension-side chamberR1 via only the notch 81 a.

The contraction-side annular plate 62 is slidably mounted on the outerperiphery of the contraction-side spacer 61. The axial direction lengthof the contraction-side annular plate 62 is shorter than the axialdirection length of the contraction-side spacer 61. Thus, thecontraction-side annular plate 62 can move in the up-down directionwhile slidingly contacting the outer periphery of the contraction-sidespacer 61. Further, the annular contraction-side plate stopper 63 isprovided to the top in FIG. 3 of the contraction-side spacer 61. Theouter diameter of the contraction-side plate stopper 63 is set to begreater than the inner diameter of the contraction-side annular plate62. The contraction-side chamber 11 is laminated on the top of thecontraction-side plate stopper 63. The inner diameter of thecontraction-side annular plate 62 is set to be smaller than the outerdiameter of the inner peripheral seat part 2 f provided to the piston 2.The outer diameter of the contraction-side annular plate 62 is set to begreater than the inner diameter of the contraction-side valve seat 2 c.The contraction-side annular plate 62 is configured such that it canmove in the axial direction (the up-down direction in FIG. 3 ) betweenthe contraction-side annular spacer 60 and the contraction-side platestopper 63.

The contraction-side annular plate 62 has a higher deflection rigiditythan that of the annular plates 81, 82 that constitute thecontraction-side leaf valve Vp. In the present embodiment, by settingthe axial direction length (thickness) of the contraction-side annularplate 62 to be greater than the axial direction length (thickness) ofthe annular plates 81, 82 of the contraction-side leaf valve Vp, therigidity of the contraction-side annular plate 62 can be increased to begreater than the rigidity of the contraction-side leaf valve Vp. Notonly can the rigidity be strengthened by the thickness, but the rigidityof the contraction-side annular plate 62 can also be increased byforming the contraction-side annular plate 62 with a material having ahigher rigidity than that of the contraction-side leaf valve Vp.

When the contraction-side annular plate 62 is compressed from the backsurface side by the pressure within the contraction-side back pressurechamber Cp and the contraction-side spool Sp, the contraction-sideannular plate 62 pushes down the contraction-side leaf valve Vp causingit to deflect. When the contraction-side leaf valve Vp deflects to thepoint at which it sits on the contraction-side valve seat 2 c, thecontraction-side annular plate 62 enters a state in which it issupported by the inner peripheral seat part 2 f and the contraction-sidevalve seat 2 c. In this state, the biasing force generated by thepressure within the contraction-side back pressure chamber Cp and thecontraction-side spool Sp is received by the contraction-side annularplate 62. Thus, any further deformation of the contraction-side leafvalve Vp is suppressed, and an excessive load is prevented from beingapplied to the contraction-side leaf valve Vp. Further, thecontraction-side annular plate 62 is slidably mounted on thecontraction-side spacer 61. Therefore, when the contraction-side leafvalve Vp deflects in a direction away from the contraction-side valveseat 2 c, the contraction-side annular plate 62 moves upward in FIG. 3relative to the contraction-side spacer 61. Thus, the deflection of thecontraction-side leaf valve Vp is not obstructed by the contraction-sideannular plate 62.

The contraction-side chamber 11 includes: a tubular mounting part 11 athat is fitted onto the outer periphery of the retaining shaft 8 a ofthe piston retaining member 8; a flange 11 b that is provided on theouter periphery at the top end in FIG. 3 of the mounting part 11 a; asliding contact tube 11 c that extends from the outer periphery of theflange 11 b toward the piston 2 side; an annular groove 11 d provided onthe inner periphery of the mounting part 11 a; and a notch 11 e thatcommunicates with the annular groove 11 d from the outer periphery ofthe mounting part 11 a. In a state in which the contraction-side chamber11 is assembled onto the retaining shaft 8 a, the annular groove 11 dopposes the extension-side pilot orifice Pe provided to the retainingshaft 8 a. The contraction-side plate stopper 63 is interposed betweenthe mounting part 11 a of the contraction-side chamber 11 and thecontraction-side spacer 61. The contraction-side plate stopper 63 may beeliminated and the upper limit of movement of the contraction-sideannular plate 62 may be restricted with the mounting part 11 a. Thereare cases in which it is necessary to adjust the position of thecontraction-side chamber 11 so that it opposes the extension-side pilotorifice Pe and the annular groove 11 d when assembling thecontraction-side chamber 11 onto the retaining shaft 8 a of the pistonretaining member 8, and in such cases, the contraction-side platestopper 63 is preferably provided between the mounting part 11 a and thecontraction-side spacer 61. The position of the contraction-side chamber11 relative to the piston retaining member 8 can be adjusted by thecontraction-side plate stopper 63.

The contraction-side spool Sp is accommodated within the sliding contacttube 11 c. The outer periphery of the contraction-side spool Spslidingly contacts the inner periphery of the sliding contact tube 11 c,and the contraction-side spool Sp is configured such that it can move inthe axial direction within the sliding contact tube 11 c. Thecontraction-side spool Sp has an annular spool main body 17, and anannular projection 18 that rises up from the inner periphery at thebottom end in FIG. 3 of the spool main body 17. The inner diameter ofthe annular projection 18 is set to be smaller than the outer diameterof the contraction-side annular plate 62, and the annular projection 18is configured such that it can abut the back surface (top surface inFIG. 3 ) of the contraction-side annular plate 62.

When the contraction-side spool Sp is assembled to the contraction-sidechamber 11 and the contraction-side chamber 11 is assembled onto theretaining shaft 8 a, the contraction-side back pressure chamber Cp isformed on the back surface side (the top side in FIG. 3 ) of thecontraction-side leaf valve Vp. The inner diameter of the spool mainbody 17 is greater than the outer diameter of the mounting part 11 a.The inner diameter of the spool main body 17 can be set so that theinner periphery of the spool main body 17 slidingly contacts the outerperiphery of the mounting part 11 a, and the contraction-side backpressure chamber Cp can be sealed by the contraction-side spool Sp.

The annular groove 11 d is provided on the inner periphery of themounting part 11 a of the contraction-side chamber 11. The mounting part11 a includes the notch 11 e that communicates with the annular groove11 d from the outer periphery of the mounting part 11 a. In a state inwhich the contraction-side chamber 11 is assembled onto the retainingshaft 8 a, the annular groove 11 d opposes the extension-side pilotorifice Pe provided to the retaining shaft 8 a, and the contraction-sideback pressure chamber Cp communicates with the extension-side pilotorifice Pe. By communicating with the extension-side pilot orifice Pe,the contraction-side back pressure chamber Cp is also in communicationwith the extension-side back pressure chamber Ce through the connectionpassage 24 formed within the vertical hole 8 d of the retaining shaft 8a and the contraction-side pilot orifice Pp.

Further, the extension-side pressure introduction passage Ie that opensfrom the outer periphery of the flange 11 b is provided to thecontraction-side chamber 11. The extension-side chamber R1 communicateswith the inside of the contraction-side back pressure chamber Cp via theextension-side pressure introduction passage Ie. An annular plate 19 islaminated on the bottom end in FIG. 3 of the flange 11 b of thecontraction-side chamber 11. A spring member 20 is interposed betweenthe annular plate 19 and the spool main body 17 of the contraction-sidespool Sp. The annular plate 19 is pressed toward the flange 11 b by thespring member 20 so that the extension-side pressure introductionpassage Ie is closed. The extension-side pressure introduction passageIe is configured so as to not generate any resistance against the flowof passing liquid.

If the shock absorber D1 extends so that the extension-side chamber R1is compressed and the pressure therein increases, the annular plate 19is pressed by this pressure so that it separates from the flange 11 b,and thereby the extension-side pressure introduction passage Ie isopened. During contraction of the shock absorber D1 in which thepressure within the contraction-side back pressure chamber Cp increaseshigher than that of the extension-side chamber R1, the annular plate 19is pressed to the flange 11 b so as to close the extension-side pressureintroduction passage Ie. In other words, the annular plate 19 functionsas a valve body of an extension-side check valve Te that permits onlythe flow of liquid from the extension-side chamber R1. By thisextension-side check valve Te, the extension-side pressure introductionpassage Ie is set to a one-way passage that permits only the flow ofliquid from the extension-side chamber R1 toward the contraction-sideback pressure chamber Cp.

As explained above, the connection passage 24 is in communication withthe inside of the accommodation part L through the annular groove 8 e,the port 8 f, and the horizontal hole 8 g provided to the pistonretaining member 8. Thus, not only are the extension-side back pressurechamber Ce and the contraction-side back pressure chamber Cp incommunication with each other via the extension-side pilot orifice Pe,the contraction-side pilot orifice Pp, and the communication passage 24,but the extension-side back pressure chamber Ce and the contraction-sideback pressure chamber Cp are also in communication with theextension-side chamber R1 via the extension-side pressure introductionpassage Ie, and in communication with the contraction-side chamber R2via the contraction-side pressure introduction passage Ip, and are alsoin communication with the accommodation part L by means of the port 8 fand the horizontal hole 8 g.

The spring member 20 functions to press the annular plate 19 to theflange 11 b. In other words, the spring member 20 constitutes theextension-side check valve Te together with the annular plate 19 whichis the valve body. The spring member 20 also functions to bias thecontraction-side spool Sp toward the contraction-side leaf valve Vp.When the contraction-side leaf valve Vp deflects so that thecontraction-side spool Sp is pushed up in the direction away from thepiston 2 (upwards in FIG. 3 ) and then the deflection of thecontraction-side leaf valve Vp subsequently terminates, thecontraction-side spool Sp is still biased by the spring member 20, andthus the contraction-side spool Sp can quickly return to its originalposition (the position shown in FIG. 3 ) following the contraction-sideleaf valve Vp. It is also possible to bias the contraction-side spool Spwith a different spring member from the spring member 20. Using the samespring member for the spring member that constitutes the extension-sidecheck valve Te and the spring member that biases the contraction-sidespool Sp is advantageous because the number of parts can be reduced andthe structure can be simplified. The outer diameter of thecontraction-side spool Sp is set to be greater than the inner diameterof the annular projection 18, and the annular projection 18 isconfigured to abut the contraction-side annular plate 62. Thecontraction-side spool Sp is constantly biased toward thecontraction-side leaf valve Vp by the pressure of the contraction-sideback pressure chamber Cp. Therefore, a spring member for the purpose ofbiasing only the contraction-side spool Sp does not have to be providedto the shock absorber D1.

The extension-side spool Se receives the pressure of the extension-sideback pressure chamber Ce and biases the extension-side leaf valve Vetoward the piston 2 via the extension-side annular plate 66. Thepressure-receiving area of the extension-side spool Se that receives thepressure of the extension-side back pressure chamber Ce is thedifference obtained by subtracting the area of a circle whose diameteris equal to the inner diameter of the annular projection 14 from thearea of a circle whose diameter is equal to the outer diameter of theextension-side spool Se. Similarly, the contraction-side spool Spreceives the pressure of the contraction-side back pressure chamber Cpand biases the contraction-side leaf valve Vp toward the piston 2 viathe contraction-side annular plate 62. The pressure-receiving area ofthe contraction-side spool Sp that receives the pressure of thecontraction-side back pressure chamber Cp is the difference obtained bysubtracting the area of a circle whose diameter is equal to the innerdiameter of the annular projection 18 from the area of a circle whosediameter is equal to the outer diameter of the contraction-side spoolSp. In the hydraulic shock absorber D1 of the present embodiment, thepressure-receiving area of the extension-side spool Se is greater thanthe pressure-receiving area of the contraction-side spool Sp.

The annular projection 14 of the extension-side spool Se abuts the backsurface of the extension-side annular plate 66, and the extension-sideannular plate 66 is mounted on the outer periphery of the extension-sidespacer 65. The pressure-receiving area in which the pressure of theextension-side back pressure chamber Ce directly acts on theextension-side annular plate 66 is obtained by subtracting the area of acircle whose diameter is equal to the outer diameter of theextension-side spacer 65 from the area of a circle whose diameter isequal to the inner diameter of the annular projection 14. Therefore, thesize of the extension-side load is obtained by multiplying the pressureof the extension-side back pressure chamber Ce by an area obtained bysubtracting the area of a circle whose diameter is equal to the outerdiameter of the extension-side spacer 65 from the area of a circle whosediameter is equal to the outer diameter of the extension-side spool Se.The extension-side leaf valve Ve is biased toward the piston 2 by theextension-side load. The extension-side annular plate 66 may beeliminated and the annular projection 14 may be directly abutted to theback surface of the extension-side leaf valve Ve.

The annular projection 18 of the contraction-side spool Sp abuts theback surface of the contraction-side annular plate 62, and thecontraction-side annular plate 62 is mounted on the outer periphery ofthe contraction-side spacer 61. The pressure-receiving area in which thepressure of the contraction-side back pressure chamber Cp directly actson the contraction-side annular plate 62 is obtained by subtracting thearea of a circle whose diameter is equal to the outer diameter of thecontraction-side spacer 61 from the area of a circle whose diameter isequal to the inner diameter of the annular projection 18. Therefore, thesize of the contraction-side load is obtained by multiplying thepressure of the contraction-side back pressure chamber Cp by an areaobtained by subtracting the area of a circle whose diameter is equal tothe outer diameter of the contraction-side spacer 61 from the area of acircle whose diameter is equal to the outer diameter of thecontraction-side spool Sp. The contraction-side leaf valve Vp is biasedtoward the piston 2 by the contraction-side load. The contraction-sideannular plate 62 may be eliminated and the annular projection 18 may bedirectly abutted to the back surface of the contraction-side leaf valveVp.

In this way, the shock absorber D1 is set such that when the pressure ofthe extension-side back pressure chamber Ce and the pressure of thecontraction-side back pressure chamber Cp are the same, the loadreceived by the extension-side leaf valve Ve from the extension-sideback pressure chamber Ce (extension-side load) is greater than the loadreceived by the contraction-side leaf valve Vp from the contraction-sideback pressure chamber Cp (contraction-side load).

In the case that the extension-side back pressure chamber Ce is closedby the extension-side spool Se and the pressure of the extension-sideback pressure chamber Ce does not directly act on the extension-sideannular plate 66, the extension-side load is determined by only thepressure-receiving area of the extension-side spool Se that receives thepressure of the extension-side back pressure chamber Ce. Similarly, inthe case that the contraction-side back pressure chamber Cp is closed bythe contraction-side spool Sp and the pressure of the contraction-sideback pressure chamber Cp does not directly act on the contraction-sideannular plate 62, the contraction-side load is determined by only thepressure-receiving area of the contraction-side spool Sp that receivesthe pressure of the contraction-side back pressure chamber Cp.Therefore, in an embodiment in which the pressures from the backpressure chambers Ce, Cp do not act directly on the extension-side leafvalve Ve and the contraction-side leaf valve Vp, in order to set theshock absorber D1 such that the extension-side load received by theextension-side leaf valve Ve from the extension-side back pressurechamber Ce is greater than the contraction-side load received by thecontraction-side leaf valve Vp from the contraction-side back pressurechamber Cp when the pressure of the extension-side back pressure chamberCe and the pressure of the contraction-side back pressure chamber Cp arethe same, it is sufficient to set the pressure-receiving area of theextension-side spool Se to be greater than the pressure-receiving areaof the contraction-side spool Sp.

In the case that the extension-side annular plate 66 and thecontraction-side annular plate 62 are eliminated, the pressure of theextension-side back pressure chamber Ce can be made to act directly onthe extension-side leaf valve Ve, and the pressure of thecontraction-side back pressure chamber Cp can be made to act directly onthe contraction-side leaf valve Vp. Further, in a structure in which theextension-side back pressure chamber Ce is closed by the extension-sidespool Se, the extension-side spool Se can be abutted to theextension-side leaf valve Ve, and in a structure in which thecontraction-side back pressure chamber Cp is closed by thecontraction-side spool Sp, the contraction-side spool Sp can be abuttedto the contraction-side leaf valve Vp. Whether or not to close theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp with the spools is a matter that can be arbitrarilyselected.

In the present embodiment, since the extension-side spool Se and thecontraction-side spool Sp are used, the pressure-receiving area in whichthe pressure of the extension-side back pressure chamber Cesubstantially acts on the extension-side leaf valve Ve can be set to begreater than the pressure-receiving area of only the extension-side leafvalve Ve. Since the difference between the pressure-receiving areas ofthe contraction-side spool Sp and the extension-side spool Se can beincreased, the difference between the extension-side load and thecontraction-side load can be increased. Thus, an extremely high degreeof freedom can be imparted to the setting widths of the extension-sideload and the contraction-side load.

During extension of the shock absorber D1, the extension-side leaf valveVe receives pressure from the extension-side chamber R1 via theextension-side passage 3 and also receives the extension-side load fromthe back surface side. If the extension-side load (a force in adirection pushing up) surpasses a force generated by the pressure of theextension-side chamber R1 (a force in a direction pushing down), theextension-side leaf valve Ve deflects. When the extension-side leafvalve Ve deflects to the point at which it abuts the extension-sidevalve seat 2 d, the extension-side passage 3 is closed. Theextension-side load acting on the extension-side leaf valve Ve duringextension of the shock absorber D1 at a certain piston speed can be setby the above-mentioned pressure-receiving area, the deflection rigidityof the extension-side leaf valve Ve, etc. In other words, by setting theabove-mentioned pressure-receiving area, the deflection rigidity of theextension-side leaf valve Ve, etc., the extension-side passage 3 can beclosed by the extension-side leaf valve Ve during extension of the shockabsorber D1 at a certain piston speed.

Similar to the extension-side leaf valve Ve, the contraction-side loadacting on the contraction-side leaf valve Vp during contraction of theshock absorber D1 at a certain piston speed can be set by theabove-mentioned pressure-receiving area, the deflection rigidity of thecontraction-side leaf valve Vp, etc. In other words, by setting theabove-mentioned pressure-receiving area, the deflection rigidity of thecontraction-side leaf valve Vp, etc., the contraction-side passage 4 canbe closed by the contraction-side leaf valve Vp during contraction ofthe shock absorber D1 at a certain piston speed.

As shown in FIG. 1 , the extension-side back pressure chamber Ce and thecontraction-side back pressure chamber Cp are on the upstream side andthe extension-side discharge passage Ee and the contraction-sidedischarge passage Ep are on the downstream side, and these are incommunication with each other via the adjustment passage Pc. Thesolenoid pressure control valve 6 is provided in the adjustment passagePc so that the pressures of the upstream extension-side back pressurechamber Ce and the contraction-side back pressure chamber Cp can becontrolled. Since the extension-side load is greater than thecontraction-side load, when controlling the pressures within theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp by the solenoid pressure control valve 6, theextension-side load can be increased even with a small pressure. If theextension-side damping force is increased, the maximum pressure to becontrolled by the solenoid pressure control valve 6 can be decreased.

In the present embodiment, the inner periphery of the extension-sidespool Se does not slidingly contact the outer periphery of the mountingpart 12 a of the extension-side chamber 12. The pressure of theextension-side back pressure chamber Ce also acts on the inside of theabutting site of the annular projection 14 on the back surface side ofthe extension-side leaf valve Ve so as to bias the extension-side leafvalve Ve. In setting the extension-side load, the setting should be madeconsidering the load that directly biases the extension-side leaf valveVe with the pressure of the extension-side back pressure chamber Ce.

Similarly, the inner periphery of the contraction-side spool Sp does notslidingly contact the outer periphery of the mounting part 11 a of thecontraction-side chamber 11. The pressure of the contraction-side backpressure chamber Cp also acts on the inside of the abutting site of theannular projection 18 on the back surface side of the contraction-sideleaf valve Vp so as to bias the contraction-side leaf valve Vp. Insetting the contraction-side load, the setting should be madeconsidering the load that directly biases the contraction-side leafvalve Vp with the pressure of the contraction-side back pressure chamberCp.

In the present embodiment, the solenoid pressure control valve 6 is setso as to close the adjustment passage Pc when not energized, and toperform pressure control when energized. A fail valve FV that bypassesthe solenoid pressure control valve 6 is provided in the adjustmentpassage Pc.

As shown in FIGS. 1 and 2 , the solenoid pressure control valve 6includes a valve seat member 30, a valve body 31 that separates from andsits on the valve seat member 30, and a solenoid Sol that providesthrust to the valve body 31 to drive the valve body 31 in the axialdirection. The valve seat member 30 has a valve accommodation tube 30 aand a valve seat 30 d. The valve body 31 separates from and sits on thevalve seat 30 d of the valve seat member 30.

The valve seat member 30 is accommodated within the accommodation partL. The position of the valve seat member 30 in the radial direction isdetermined by inserting the valve accommodation tube 30 a into the innerperiphery of an annular valve housing 32 that is laminated on the topend in FIG. 2 of the flange 8 b. The valve housing 32 is fitted into thesocket 8 c of the piston retaining member 8.

As shown in FIG. 2 , the valve housing 32 is formed in an annular shape.The valve housing 32 includes: an annular window 32 a provided on thetop end in FIG. 2 ; a port 32 b that opens from the annular window 32 aand communicates with the bottom end in FIG. 2 ; a notched groove 32 cthat opens from the inner periphery at the top end in FIG. 2 andcommunicates with the port 32 b; a groove 32 d provided in the outerperiphery along the axial direction; and a valve seat 32 e of the failvalve FV. The valve seat 32 e is formed in an annular shape so as tosurround the outer periphery of the annular window 32 a.

In a state in which the valve housing 32 is inserted into the socket 8 cand is laminated on the top end in FIG. 2 of the flange 8 b, the port 32b opposes an opening formed on a top end surface of the flange 8 b ofthe port 8 f, and the port 32 b and the notched groove 32 c are incommunication with the port 8 f. Further, the groove 32 d opposes thegroove 8 j formed in the flange 8 b, and the groove 32 d and the groove8 j are in communication with each other.

The port 32 b and the notched groove 32 c are in communication with thecommunication passage 24 via the annular groove 8 e, the port 8 f, andthe horizontal hole 8 g. Further, the port 32 b and the notched groove32 c are in communication with the extension-side back pressure chamberCe and the contraction-side back pressure chamber Cp via thecommunication passage 24, the extension-side pilot orifice Pe, and thecontraction-side pilot orifice Pp. The groove 32 d is in communicationwith the inside of the separator 23 via the groove 8 j and with thecontraction-side chamber R2 via the extension-side discharge passage Eeformed by the check valve 25. Further, the groove 32 d is incommunication with the extension-side chamber R1 via the through hole 9c, the recess 8 k, the through hole 8 m, and the contraction-sidedischarge passage Ep formed by the check valve 22.

The valve accommodation tube 30 a of the tubular valve seat member 30 isaccommodated within the valve housing 32. The valve seat member 30includes: the closed-bottom cylindrical valve accommodation tube 30 a; athrough hole 30 c that opens from the side of the valve accommodationtube 30 a and communicates with the inside thereof; and the annularvalve seat 30 d that projects toward the axial direction from the topend in FIG. 2 of the valve accommodation tube 30 a. The valveaccommodation tube 30 a has a flange 30 b on the outer periphery at thetop end in FIG. 2 .

The valve body 33 of the fail valve FV is mounted on the outer peripheryof the valve accommodation tube 30 a of the valve seat member 30. Thevalve body 33 consists of an annular leaf valve. In a state in which thevalve accommodation tube 30 a is inserted into the valve housing 32 andthe valve seat member 30 is assembled to the valve housing 32, the innerperiphery of the valve body 33 is sandwiched by the flange 30 b of thevalve seat member 30 and the inner periphery at the top end in FIG. 2 ofthe valve housing 32, and by this sandwiching, the valve body 33 isfixed to the valve seat member 30. The outer peripheral side of thevalve body 33 sits on the annular valve seat 32 e provided to the valvehousing 32 in a state in which an initial deflection is provided, andthe valve body 33 blocks the annular window 32 a. The valve body 33deflects when the pressure acting on the inside of the annular window 32a via the port 32 b reaches a valve-opening pressure. As a result, theannular window 32 b is opened, and the port 32 b communicates with theextension-side discharge passage Ee and the contraction-side dischargepassage Ep. In this way, the fail valve FV is formed by the valve body33 and the valve seat 32 e.

Further, in a state in which the valve accommodation tube 30 a isinserted into the valve housing 32 and the valve seat member 30 isassembled to the valve housing 32, the notched groove 32 c provided tothe valve housing 32 opposes the through hole 30 c provided to the valveaccommodation tube 30 a. The extension-side back pressure chamber Ce andthe contraction-side back pressure chamber Cp are in communication withthe inside of the valve accommodation tube 30 a via the port 32 b.

An annular valve fixing member 35 is laminated on the top in FIG. 1 ofthe valve seat member 30. The valve fixing member 35 abuts the top endin FIG. 1 of the flange 30 b. Further, the solenoid Sol accommodatedwithin the solenoid valve accommodation tube 9 is disposed on the top inFIG. 1 of the valve fixing member 35. When the solenoid valveaccommodation tube 9 and the piston retaining member 8 are integrated byscrewing, the valve housing 32, the valve body 33, the valve seat member30, the valve fixing member 35, and the solenoid Sol are sandwiched bythe solenoid valve accommodation tube 9 and the piston retaining member8. A notched groove 35 a is provided in the valve fixing member 35. Evenin a state in which the valve fixing member 35 abuts the flange 30 b ofthe valve seat member 30, a space on the inner peripheral side of thevalve fixing member 35 communicates with a space on the outer peripheralside of the valve seat member 30 by means of the notched groove 35 a.The space on the inner peripheral side of the valve fixing member 35 andthe space on the outer peripheral side of the valve seat member 30 maycommunicate with each other via a hole such as a port instead of thenotched groove 35 a.

The solenoid Sol includes: a closed-top cylindrical mold stator 36, afirst fixed iron core 38 that is fitted into the inner periphery of themold stator 36; an annular second fixed iron core 39 that is laminatedon the bottom end in FIG. 1 of the mold stator 36; a filler ring 40 thatis interposed between the first fixed iron core 38 and the second fixediron core 39; a cylindrical movable iron core 41 that is disposed suchthat it can move in the axial direction on the inner peripheral side ofthe first fixed iron core 38 and the second fixed iron core 39; and ashaft 42 that is fixed to the inner periphery of the movable iron core41. The mold stator 36 is formed by integrating, using a molded resin, acoil 37 and a harness H that energizes the coil 37. The first fixed ironcore 38 is formed in a closed-top cylindrical shape. The filler ring 40has a magnetic air gap. By energizing the coil 37, the movable iron core41 is suctioned, and thereby a thrust oriented downward in FIG. 1 can beprovided to the shaft 42.

Further, the valve body 31 of the solenoid valve is slidingly insertedinto the valve seat member 30. In detail, the valve body 31 includes: asmall-diameter part 31 a that is slidably inserted into the valveaccommodation tube 30 a of the valve seat member 30; a large-diameterpart 31 b that is provided to the small-diameter part 31 a on theopposite side (the top side in FIG. 2 ) of the valve seat member 30; anannular recess 31 c that is provided between the small-diameter part 31a and the large-diameter part 31 b; a flange-shaped spring receivingpart 31 d that is provided on the outer periphery of the edge of thelarge-diameter part 31 b on the opposite side of the valve seat member30; a connection passage 31 e that penetrates from the distal end to therear end of the valve body 31; and an orifice 31 f that is provided inthe connection passage 31 e. The large-diameter part 31 b is notinserted into the valve accommodation tube 30 a.

As described above, the valve body 31 of the solenoid valve has thelarge-diameter part 31 b, which has an outer diameter that is greaterthan the outer diameter of the small-diameter part 31 a, on the oppositeside of the valve seat member 30 with the recess 31 c as a boundarytherebetween. The valve body 31 includes a seating part 31 g thatopposes the valve seat 30 d of the control valve on the bottom end inFIG. 2 of the large-diameter part 31 b. When the valve body 31 of thesolenoid valve moves in the axial direction relative to the valve seatbody 30, the seating part 31 g separates from and sits on the valve seat30 d of the control valve. In other words, the solenoid pressure controlvalve 6 includes the valve body 31 and the valve seat member 30. Whenthe seating part 31 g sits on the valve seat 30 d of the control valve,the solenoid pressure control valve 6 closes.

A coil spring 34, which biases the valve body 31 of the solenoid valvein a direction away from the valve seat member 30, is interposed betweenthe flange 30 b of the valve seat member 30 and the spring receivingpart 31 d. Therefore, the valve body 31 of the solenoid valve isconstantly biased by the coil spring 34 in a direction away from thevalve seat member 30. The shock absorber D1 includes the solenoid Solthat exerts a thrust against the biasing force of the coil spring 34. Ifthe thrust against the coil spring 34 from the solenoid Sol does notact, the valve body 31 is positioned at a position farthest away fromthe valve seat member 30. In this case, the valve body 31 of thesolenoid valve is biased in a direction away from the valve seat member30 utilizing the coil spring 34, but an elastic body capable of exertinga biasing force other than the coil spring 34 can be used.

In a state in which the valve body 31 of the solenoid valve is farthestaway from the valve seat member 30, the small-diameter part 31 a opposesthe through hole 30 c and the through hole 30 c is blocked. In a statein which the solenoid Sol is energized so that the valve body 31 movesby a prescribed amount toward the valve seat member side from theposition farthest away from the valve seat member 30, the recess 31 cconstantly opposes the through hole 30 c and the through hole 30 c isopened.

In a state in which the valve body 31 of the solenoid valve opens thethrough hole 30 c and the seating part 31 g separates from the valveseat 30 d of the control valve, the through hole 30 c is incommunication with the extension-side discharge passage Ee and thecontraction-side discharge passage Ep via the recess 31 c of the valvebody 31 of the solenoid valve and the notched groove 35 a provided tothe valve fixing member 35. By adjusting the thrust of the solenoid Sol,the force that biases the valve body 31 of the solenoid valve toward thevalve seat member 30 side can be controlled. If the action of thepressure upstream of the solenoid pressure control valve 6 and the forcegenerated by the coil spring 34 that pushes the valve body 31 of thesolenoid valve upward in FIG. 2 surpass the force generated by thesolenoid Sol that pushes down the valve body 31 of the solenoid valve,the solenoid pressure control valve 6 opens. In other words, thepressure on the upstream side of the solenoid pressure control valve 6can be controlled according to the thrust of the solenoid Sol. Theupstream of the solenoid pressure control valve 6 communicates with theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp via the adjustment passage Pc, and thus thepressures of the extension-side back pressure chamber Ce and thecontraction-side back pressure chamber Cp can be controlled by thesolenoid pressure control valve 6. Further, the downstream of thesolenoid pressure control valve 6 communicates with the extension-sidedischarge passage Ee and the contraction-side discharge passage Ep.During extension of the hydraulic shock absorber D1, liquid passingthrough the solenoid pressure control valve 6 is discharged to thecontraction-side chamber R2 on the low-pressure side. During contractionof the hydraulic shock absorber D1, liquid passing through the solenoidpressure control valve 6 is discharged to the extension-side chamber R1on the low-pressure side. Therefore, the adjustment passage Pc is formedby the annular groove 8 e, the port 8 f, the horizontal hole 8 g, theport 32 b, the notched groove 32 c, a portion of the accommodation partL, and the groove 32 d.

The solenoid pressure control valve 6 includes a blocked position inwhich the through hole 30 c of the valve seat member 30 is blocked bythe small-diameter part 31 a of the valve body 31 of the solenoid valveduring a failure in which the solenoid Sol cannot be energized. In otherwords, the solenoid pressure control valve 6 functions not only as apressure control valve but also as an opening/closing valve. The failvalve FV is configured so as to open/close the annular window 32 a thatcommunicates with the port 32 b. The valve-opening pressure of the failvalve FV is set to a pressure exceeding the upper limit pressure thatcan be controlled by the solenoid pressure control valve 6. The failvalve FV is configured so as to be able to bypass the solenoid pressurecontrol valve 6 and allow the port 32 b to communicate with theextension-side discharge passage Ee and contraction-side dischargepassage Ep. If the pressure on the upstream side of the solenoidpressure control valve 6 exceeds the control upper limit pressure, thefail valve is configured so as to open so that the pressures of theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp can be controlled to the valve-opening pressure ofthe fail valve FV. Therefore, for example, if the solenoid pressurecontrol valve 6 enters the blocked position during a failure, thepressures of the extension-side back pressure chamber Ce and thecontraction-side back pressure chamber Cp are controlled by the failvalve FV.

When the valve body 31 of the solenoid valve is inserted into the valveaccommodation tube 30 a of the valve seat member 30, a space K is formedwithin the valve accommodation tube 30 a more toward the distal end sidethan the through hole 30 c. The space K is in communication with theoutside of the valve body of the solenoid valve via the connectionpassage 31 e and the orifice 31 f provided to the valve body 31 of thesolenoid valve. Therefore, when the valve body 31 of the solenoid valvemoves in the axial direction (the up-down direction in FIG. 2 ) relativeto the valve seat member 30, the space K functions as a dash pot. Thus,steep displacement of the valve body 31 of the solenoid valve can besuppressed, and vibrational movement of the valve body 31 of thesolenoid valve can be suppressed.

Next, the operation of the shock absorber D1 will be explained. First, acase in which the damping force characteristics of the shock absorber D1are set to soft, i.e. a case in which the biasing force that isgenerated by the biasing part and biases the extension-side leaf valveVe and the contraction-side leaf valve Vp is decreased and the dampingcoefficient is decreased, will be explained. In order to make thedamping force characteristics soft, the biasing force generated by thebiasing part is controlled so that the extension-side leaf valve Ve andthe contraction-side leaf valve Vp do not sit on the correspondingextension-side valve seat 2 d and the contraction-side valve seat 2 c.Specifically, the resistance applied by the solenoid pressure controlvalve 6 to the passing liquid is decreased by energizing the solenoidSol.

In this state, even if the extension-side leaf valve Ve deflects due tothe biasing force generated by the biasing part, the extension-side leafvalve Ve does not sit on the extension-side valve seat 2 d and a gap isformed between the two. The same applies to the contraction-side leafvalve Vp, such that even if the contraction-side leaf valve Vp deflectsdue to the biasing force generated by the biasing part, thecontraction-side leaf valve Vp does not sit on the contraction-sidevalve seat 2 c and a gap is formed between the two.

In this state, if the shock absorber D1 extends and the piston 2 movesupward in FIG. 1 , the liquid within the extension-side chamber R1 thatis compressed pushes the extension-side leaf valve Ve causing it todeflect. The liquid within the extension-side chamber R1 passes throughthe extension-side passage 3 and moves to the contraction-side chamberR2 that is expanded. Since a gap is formed between the extension-sideleaf valve Ve and the extension-side valve seat 2 d, a larger flow patharea is secured compared to the state in which the extension-side leafvalve Ve sits on the extension-side valve seat 2 d and theextension-side passage 3 communicates with the contraction-side chamberR2 via only the notch 71 a. Therefore, as indicated by the line B inFIG. 4 , the shock absorber D1 can reduce the damping force when thepiston speed is in a low-speed region compared to the damping forcegenerated by a conventional shock absorber as shown by the line A.

When the pressure within the extension-side chamber R1 rises inaccordance with the extension of the shock absorber D1, theextension-side leaf valve Ve deflects. The amount of this deflection isdetermined by the balance between a force that is generated by thepressure of the extension-side chamber R1 and that attempts to make theextension-side leaf valve Ve deflect from the extension-side passage 3side, and the total of a force that is generated by the spring reactionforce possessed by the extension-side leaf valve Ve itself according tothe above-mentioned amount of deflection and that attempts to return theextension-side leaf valve Ve to the extension-side valve seat 2 d sideand the extension-side load generated by the biasing part. Theextension-side leaf valve Ve opens the extension-side passage 3 bydeflecting.

The liquid within the extension-side chamber R1 pushes and opens theextension-side check valve Te. The liquid within the extension-sidechamber R1 passes through the extension-side pressure introductionpassage Ie and flows to the adjustment passage Pc. The liquid that haspassed through the adjustment passage Pc pushes and opens the checkvalve 25, and is discharged to the contraction-side chamber R2 on thelow-pressure side via the extension-side discharge passage Ee. Theextension-side pilot orifice Pe applies resistance when liquid passestherethrough to cause a pressure loss. In a state in which the liquid isflowing, the pressure downstream of the adjustment passage Pc decreaseslower than the pressure of the extension-side chamber R1, and thus thecheck valve 22 provided to the contraction-side discharge passage Epdoes not open and remains closed.

The extension-side pressure introduction passage Ie not onlycommunicates with the contraction-side back pressure chamber Cp, butalso communicates with the extension-side back pressure chamber Ce viathe communication passage 24. Since the contraction-side pressureintroduction passage Ip is closed by the contraction-side check valveTp, during extension of the shock absorber D1, the pressure within theextension-side back pressure chamber Ce can be increased higher thanthat of the contraction-side chamber R2. The pressure of thecontraction-side back pressure chamber Cp becomes higher than thepressure of the contraction-side chamber R2 on the low-pressure side.The gap between the contraction-side leaf valve Vp and thecontraction-side valve seat 2 c acts as an orifice until thecontraction-side leaf valve Vp deflects due to the pressure of theextension-side chamber R1 and the pressure of the contraction-side backpressure chamber Cp so that the contraction-side leaf valve Vp sits onthe contraction-side valve seat 2 c. During extension of the shockabsorber D1, liquid does not need to flow through the contraction-sidepassage 4, and thus there is no problem even if the contraction-sideleaf valve Vp deflects due to the pressure of the extension-side chamberR1 and the pressure of the contraction-side back pressure chamber Cp soas to sit on the contraction-side valve seat 2 c causing thecontraction-side passage 4 to be closed.

The solenoid pressure control valve 6 is provided in the adjustmentpassage Pc as explained above. When the solenoid Sol of the solenoidpressure control valve 6 is energized so as to control the pressure onthe upstream side of the adjustment passage Pc, the pressure within theextension-side back pressure chamber Ce can be adjusted and theextension-side load can be controlled to a desired load. Given theabove, the opening degree of the extension-side leaf valve Ve can becontrolled by the solenoid pressure control valve 6, and thereby theextension-side damping force during extension of the shock absorber D1can be controlled.

If the shock absorber D1 contracts and the piston 2 moves downward inFIG. 1 , the liquid within the contraction-side chamber R2 that iscompressed pushes the contraction-side leaf valve Vp causing it todeflect. The liquid within the contraction-side chamber R2 passesthrough the contraction-side passage 4 and moves to the extension-sidechamber R1 that is expanded. Since a gap is formed between thecontraction-side leaf valve Vp and the contraction-side valve seat 2 c,a larger flow path area is secured compared to the state in which thecontraction-side leaf valve Vp sits on the contraction-side valve seat 2c and the contraction-side passage 4 communicates with theextension-side chamber R1 via only the notch 81 a. Therefore, asindicated by the line D in FIG. 4 , the shock absorber D1 can reduce thedamping force when the piston speed is in a low-speed region compared tothe damping force generated by a conventional shock absorber as shown bythe line C.

When the pressure within the contraction-side chamber R2 rises inaccordance with the contraction of the shock absorber D1, thecontraction-side leaf valve Vp deflects. The amount of this deflectionis determined by the balance between a force that is generated by thepressure of the contraction-side chamber R2 and that attempts to makethe contraction-side leaf valve Vp deflect from the contraction-sidepassage 4 side, and the total of a force that is generated by the springreaction force possessed by the contraction-side leaf valve Vp itselfaccording to the above-mentioned amount of deflection and that attemptsto return the contraction-side leaf valve Vp to the contraction-sidevalve seat 2 c side and the contraction-side load generated by thebiasing part. The contraction-side leaf valve Vp opens thecontraction-side passage 4 by deflecting.

The liquid within the contraction-side chamber R2 pushes and opens thecontraction-side check valve Tp. The liquid within the contraction-sidechamber R2 passes through the contraction-side pressure introductionpassage Ip and flows to the adjustment passage Pc. The liquid that haspassed through the adjustment passage Pc pushes and opens the checkvalve 22, and is discharged to the extension-side chamber R1 on thelow-pressure side via the contraction-side discharge passage Ep. Thecontraction-side pilot orifice Pp applies resistance when liquid passestherethrough to cause a pressure loss. In a state in which the liquid isflowing, the pressure downstream of the adjustment passage Pc decreaseslower than the pressure of the contraction-side chamber R2, and thus thecheck valve 25 provided to the extension-side discharge passage Ee doesnot open and remains closed.

The contraction-side pressure introduction passage Ip not onlycommunicates with the extension-side back pressure chamber Ce, but alsocommunicates with the contraction-side back pressure chamber Cp via thecommunication passage 24. Since the extension-side pressure introductionpassage Ie is closed by the extension-side check valve Te, duringcontraction of the shock absorber D1, the pressure within thecontraction-side back pressure chamber Cp can be increased higher thanthat of the extension-side chamber R1. The pressure of theextension-side back pressure chamber Ce becomes higher than the pressureof the extension-side chamber R1 on the low-pressure side. The gapbetween the extension-side leaf valve Ve and the extension-side valveseat 2 d acts as an orifice until the extension-side leaf valve Vedeflects due to the pressure of the contraction-side chamber R2 and thepressure of the extension-side back pressure chamber Ce so that theextension-side leaf valve Ve sits on the extension-side valve seat 2 d.During contraction of the shock absorber D1, liquid does not need toflow through the extension-side passage 3, and thus there is no problemeven if the extension-side leaf valve Ve deflects due to the pressure ofthe contraction-side chamber R2 and the pressure of the extension-sideback pressure chamber Ce so as to sit on the extension-side valve seat 2d causing the extension-side passage 3 to be closed.

The solenoid pressure control valve 6 is provided in the adjustmentpassage Pc as explained above. When the solenoid Sol of the solenoidpressure control valve 6 is energized so as to control the pressure onthe upstream side of the adjustment passage Pc, the pressure within thecontraction-side back pressure chamber Cp can be adjusted and thecontraction-side load can be controlled to a desired load. Given theabove, the opening degree of the contraction-side leaf valve Vp can becontrolled by the solenoid pressure control valve 6, and thereby thecontraction-side damping force during contraction of the shock absorberD1 can be controlled.

Next, a case in which the damping force characteristics of the shockabsorber D1 are set to hard, i.e. a case in which the biasing force thatis generated by the biasing part and biases the extension-side leafvalve Ve and the contraction-side leaf valve Vp is increased and thedamping coefficient is increased, will be explained. In order to makethe damping force characteristics hard, the biasing force generated bythe biasing part is controlled so that the extension-side leaf valve Veand the contraction-side leaf valve Vp sit on the correspondingextension-side valve seat 2 d and the contraction-side valve seat 2 c.Specifically, the solenoid Sol is energized so as to increase theresistance applied by the solenoid pressure control valve 6 to thepassing liquid.

In this state, the extension-side leaf valve Ve deflects due to thebiasing part and sits on the extension-side valve seat 2 d, and no gapis formed between the two. The same applies to the contraction-side leafvalve Vp, such that the contraction-side leaf valve Vp deflects due tothe biasing part and sits on the contraction-side valve seat 2 c, and nogap is formed between the two.

When the piston 2 moves upward in FIG. 1 at a low piston speed and theshock absorber D1 extends, the extension-side leaf valve Ve does notseparate from the extension-side valve seat 2 d even if theextension-side leaf valve Ve receives pressure from the extension-sidechamber R1 via the extension-side passage 3. Therefore, theextension-side leaf valve Ve allows the extension-side chamber R1 tocommunicate with the contraction-side chamber R2 via the notch 71 aexcluding the adjustment passage Pc. In this state, the shock absorberD1 applies resistance mainly with the notch 71 a functioning as anorifice against the flow of liquid passing through the extension-sidepassage 3. Accordingly, the shock absorber D1 can exert a larger dampingforce compared to the damping force that is generated in the state inwhich a gap is formed between the extension-side leaf valve Ve and theextension-side valve seat 2 d.

On the other hand, if the piston speed is high, the pressure of theextension-side chamber R1 that acts on the extension-side leaf valve Vevia the extension-side passage 3 increases. If the force in a directioncausing the extension-side leaf valve Ve to separate from theextension-side valve seat 2 d that is generated by the pressure of theextension-side chamber R1 surpasses the biasing force of the biasingpart, the extension-side leaf valve Ve deflects and the extension-sideannular plate 66 and the extension-side spool Se are pushed downward inFIG. 3 and separate from the extension-side valve seat 2 d. Since thebiasing force generated by the biasing part is large compared to thestate in which the damping force characteristics are set to be soft, theamount of deflection of the extension-side leaf valve Ve is small. Asindicated by the line E in FIG. 4 , even at the same piston speed, theshock absorber D1 exerts a higher damping force when set to hard thanwhen set to soft.

Similar to the case in which the damping force characteristics are setto soft, the liquid within the extension-side chamber R1 pushes andopens the extension-side check valve Te and passes through theextension-side pressure introduction chamber Ie to flow into theadjustment passage Pc. By controlling the pressure on the upstream sideof the adjustment passage Pc with the solenoid pressure control valve 6provided to the adjustment passage Pc, similar to when set to soft, thepressure within the extension-side back pressure chamber Ce can beadjusted and the extension-side load can be controlled to a desiredload, and the opening degree of the extension-side leaf valve Ve can becontrolled. Thereby, the damping force (extension-side damping force)during extension of the shock absorber D1 in which the damping forcecharacteristics have been set to hard can be controlled.

When the piston 2 moves downward in FIG. 1 at a low piston speed and theshock absorber D1 contracts, the contraction-side leaf valve Vp does notseparate from the contraction-side valve seat 2 c even if thecontraction-side leaf valve Vp receives pressure from thecontraction-side chamber R2 via the contraction-side passage 4.Therefore, the contraction-side leaf valve Vp allows thecontraction-side chamber R2 to communicate with the extension-sidechamber R1 via the notch 81 a excluding the adjustment passage Pc. Inthis state, the shock absorber D1 applies resistance mainly with thenotch 81 a functioning as an orifice against the flow of liquid passingthrough the contraction-side passage 4. Accordingly, the shock absorberD1 can exert a larger damping force compared to the damping force thatis generated in the state in which a gap is formed between thecontraction-side leaf valve Vp and the contraction-side valve seat 2 c.

On the other hand, if the piston speed is high, the pressure of thecontraction-side chamber R2 that acts on the contraction-side leaf valveVp via the contraction-side passage 4 increases. If the force in adirection causing the contraction-side leaf valve Vp to separate fromthe contraction-side valve seat 2 c that is generated by the pressure ofthe contraction-side chamber R2 surpasses the biasing force of thebiasing part, the contraction-side leaf valve Vp deflects and thecontraction-side annular plate 62 and the contraction-side spool Sp arepushed upward in FIG. 3 and separate from the contraction-side valveseat 2 c. Since the biasing force generated by the biasing part is largecompared to the state in which the damping force characteristics are setto be soft, the amount of deflection of the contraction-side leaf valveVp is small. As indicated by the line F in FIG. 4 , even at the samepiston speed, the shock absorber D1 exerts a higher damping force whenset to hard than when set to soft.

Similar to the case in which the damping force characteristics are setto soft, the liquid within the contraction-side chamber R2 pushes andopens the contraction-side check valve Tp and passes through thecontraction-side pressure introduction chamber Ip to flow into theadjustment passage Pc. By controlling the pressure on the upstream sideof the adjustment passage Pc with the solenoid pressure control valve 6provided to the adjustment passage Pc, similar to when set to soft, thepressure within the contraction-side back pressure chamber Cp can beadjusted and the contraction-side load can be controlled to a desiredload, and the opening degree of the contraction-side leaf valve Vp canbe controlled. Thereby, the damping force (contraction-side dampingforce) during contraction of the shock absorber D1 in which the dampingforce characteristics have been set to hard can be controlled.

In this way, in the damping valve and shock absorber D1 of the presentembodiment, gaps are provided between the leaf valves Ve, Vp and thevalve seats 2 c, 2 d. Therefore, when the biasing force generated by thebiasing part is reduced and the damping characteristics are set to soft,compared to a conventional damping valve and shock absorber using afixed orifice, the flow passage area can be increased and the dampingforce can be decreased when the piston speed is in a low-speed region.Further, in the damping valve and shock absorber D1, when set to hard,the leaf valves Ve, Vp can be made to sit on the valve seats 2 c, 2 d,and thus the damping force variable width can also be secured.

Thus, according to the damping valve and the shock absorber of thepresent embodiment, the damping force when the piston speed is in alow-speed region can be decreased and the damping force adjustment widthcan be expanded.

In the case that the damping force characteristics of the shock absorberD1 according to the present embodiment are switched from soft to hardduring the extension operation, the gap between the extension-side leafvalve Ve and the extension-side valve seat 2 d gradually decreases dueto the increase in pressure within the extension-side back pressurechamber Ce, and thus the extension-side leaf valve Ve sits on theextension-side valve seat 2 d. In the case that the damping forcecharacteristics of the shock absorber D1 are switched from soft to hardduring the contraction operation, the gap between the contraction-sideleaf valve Vp and the contraction-side valve seat 2 c graduallydecreases due to the increase in pressure within the contraction-sideback pressure chamber Cp, and thus the contraction-side leaf valve Vpsits on the contraction-side valve seat 2 c. Conversely, in the casethat the damping force characteristics of the shock absorber D1according to the present embodiment are switched from hard to softduring the extension operation, the gap between the extension-side leafvalve Ve and the extension-side valve seat 2 d gradually increases dueto the decrease in pressure within the extension-side back pressurechamber Ce. In the case that the damping force characteristics of theshock absorber D1 according to the present embodiment are switched fromhard to soft during the contraction operation, the gap between thecontraction-side leaf valve Vp and the contraction-side valve seat 2 cgradually increases due to the decrease in pressure within thecontraction-side back pressure chamber Cp. Therefore, when the dampingforce characteristics of the shock absorber D1 are switched from soft tohard or from hard to soft, any sudden changes in the damping forcecharacteristics of the shock absorber D1 are mitigated. In a vehicleequipped with the shock absorber D1, sudden changes in the damping forcecharacteristics are mitigated, and thus shocks during switching of thedamping force characteristics are not perceived by the passengers, andthe riding comfort of the vehicle can be improved.

The extension-side annular plate 66 is laminated on the back surface ofthe extension-side leaf valve Ve, and the extension-side annular plate66 is slidingly mounted on the outer periphery of the extension-sidespacer 65. The contraction-side annular plate 62 is laminated on theback surface of the contraction-side leaf valve Vp, and thecontraction-side annular plate 62 is slidingly mounted on the outerperiphery of the contraction-side spacer 61. Therefore, by setting therigidity of the extension-side annular plate 66 to be higher than therigidity of the extension-side leaf valve Ve and setting the rigidity ofthe contraction-side annular plate 62 to be higher than the rigidity ofthe contraction-side leaf valve Vp, the biasing force generated by thebiasing part can be received by the extension-side annular plate 66 andthe contraction-side annular plate 62. Thus, deformation of theextension-side leaf valve Ve and the contraction-side leaf valve Vp canbe suppressed, and deterioration of the extension-side leaf valve Ve andthe contraction-side leaf valve Vp can be suppressed.

The extension-side annular plate 66 is slidingly mounted on the outerperiphery of the extension-side spacer 65 that is laminated on the backsurface of the extension-side leaf valve Ve, and the contraction-sideannular plate 62 is slidingly mounted on the outer periphery of thecontraction-side spacer 61 that is laminated on the back surface of thecontraction-side leaf valve Vp. The inner diameter of the extension-sideannular plate 66 is smaller than the outer diameter of the innerperipheral seat part 2 h of the piston 2, and the outer diameter of theextension-side annular plate 66 is greater than the inner diameter ofthe extension-side valve seat 2 d. Further, the inner diameter of thecontraction-side annular plate 62 is smaller than the outer diameter ofthe inner peripheral seat part 2 f of the piston 2, and the outerdiameter of the contraction-side annular plate 62 is greater than theinner diameter of the contraction-side valve seat 2 c. Therefore, thepressure on the back surfaces of the extension-side leaf valve Ve andthe contraction-side leaf valve Vp can be received by the extension-sideannular plate 66 and the contraction-side annular plate 62. Accordingly,by providing the extension-side annular plate 66 and thecontraction-side annular plate 62 to the shock absorber D1, excessiveloads on the extension-side leaf valve Ve and the contraction-side leafvalve Vp can be prevented, and the rigidity of the extension-side leafvalve Ve and the contraction-side leaf valve Vp can be further reduced,and thus leaf valves with lower deflection rigidity can be utilized.Therefore, a lower damping force can be exerted by the shock absorberD1.

Further, the biasing part biases the leaf valves Ve, Vp using either oneor both of the pressures of the extension-side chamber R1 and thecontraction-side chamber R2 within the shock absorber D1. Therefore, theleaf valves Ve, Vp can be biased without using a biasing forcegeneration source, and the biasing force can be changed by controllingthe pressure.

In a shock absorber for a vehicle, it is necessary to make theextension-side damping force during the extension operation greater thanthe contraction-side damping force during the contraction operation. Inthe shock absorber D1 that is set to a single-rod type, thepressure-receiving area that receives the pressure of the extension-sidechamber R1 is an area obtained by subtracting the cross-section area ofthe rod member 10 from the cross-section area of the piston 2. Thus, itis necessary to make the pressure of the extension-side chamber R1during the extension operation much greater than the pressure of thecontraction-side chamber R2 during the contraction operation.

In contrast, in the shock absorber D1 according to the presentembodiment, in the case that the extension-side back pressure chamber Ceand the contraction-side back pressure chamber Cp are at equalpressures, the extension-side load that biases the extension-side leafvalve Ve is greater than the contraction-side load that biases thecontraction-side leaf valve Vp. Further, in the present embodiment, theextension-side spool Se is used. Compared to a structure in which theextension-side spool Se is not used and the pressure of theextension-side back pressure chamber Ce is merely made to act on theback surface side of the extension-side leaf valve Ve, thepressure-receiving area of the extension-side spool Se that receives thepressure of the extension-side back pressure chamber Ce can be madegreater than the back surface area of the extension-side leaf valve Ve.Therefore, a large extension-side load can be made to act on theextension-side leaf valve Ve. Further, by using the extension-side spoolSe and the contraction-side spool Sp, the degree of freedom fordesigning the extension-side load and the contraction-side load can beimproved.

Accordingly, in the shock absorber D1 of the present embodiment, in thecase that it is necessary to greatly increase the extension-side load inorder to adjust the extension-side damping force during the extensionoperation, it is possible to make settings so as to output a largeextension-side load even if the pressure of the extension-side backpressure chamber Ce is small. Thus, the control width of theextension-side damping force can be secured even without using a largesolenoid Sol.

Instead of performing pressure control of the extension-side backpressure chamber Ce and the contraction-side back pressure chamber Cp bydriving independent valve bodies, by making the extension-side loadgreater than the contraction-side load, the control width of theextension-side damping force can be secured even if the pressures of theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp are controlled in communication with each other.Thus, it is sufficient to provide a single valve body 31 of the solenoidvalve to the solenoid pressure control valve 6. Therefore, the structurebecomes extremely simple and the costs can also be lowered.

Due to the above, the size of the solenoid Sol in the solenoid pressurecontrol valve 6 can be decreased, and in addition, the structure of thesolenoid pressure control valve 6 is simplified and the size of theshock absorber D1 does not increase even if the solenoid pressurecontrol valve 6 is utilized in the piston part of the shock absorber D1.Thus, according to the shock absorber D1 of the present embodiment, thestructure of the shock absorber D1 is simplified and the size thereof isreduced, and the installation into the vehicle is not negativelyaffected. Further, since the extension-side damping force can beincreased even if the solenoid Sol does not exert a large thrust, thepower consumption when increasing the damping force can be reduced andthus power saving can be achieved.

Since the pressure-receiving area of the extension-side spool Se thatreceives the pressure of the extension-side back pressure chamber Ce isconfigured to be greater than the pressure-receiving area of thecontraction-side spool Sp that receives the pressure of thecontraction-side back pressure chamber Cp, the extension-side load canbe easily configured to be greater than the contraction-side load.

The extension-side back pressure chamber Ce and the contraction-sideback pressure chamber Cp communicate with each other through thecommunication passage 24 via the contraction-side resistance element andthe extension-side resistance element. The contraction-side pressureintroduction passage Ip introduces liquid from the contraction-sidechamber R2 to the extension-side back pressure chamber Ce with hardlyany resistance. Therefore, when the shock absorber D1 switches from theextension operation to the contraction operation, the pressure withinthe contraction-side chamber R2 is quickly introduced into theextension-side back pressure chamber Ce. Thus, the extension-side spoolSe presses the extension-side leaf valve Ve by means of the pressurewithin the extension-side back pressure chamber Ce and the biasing bythe spring member 16 so that the extension-side leaf valve Ve can bequickly seated on the extension-side valve seat 2 d to close theextension-side passage 3. The extension-side pressure introductionpassage Ie also introduces liquid from the extension-side chamber R1 tothe contraction-side back pressure chamber Cp with hardly anyresistance. Therefore, when the shock absorber D1 switches from thecontraction operation to the extension operation, the pressure withinthe extension-side chamber R1 is quickly introduced into thecontraction-side back pressure chamber Cp. Thus, the contraction-sidespool Sp presses the contraction-side leaf valve Vp by means of thepressure within the contraction-side back pressure chamber Cp and thebiasing by the spring member 20 so that the contraction-side leaf valveVp can be quickly seated on the contraction-side valve seat 2 c to closethe contraction-side passage 4. In this way, in the shock absorber D1,even in a situation in which the extension/contraction speed is high andthe switching between the extension/contraction operations occursinstantaneously, a desired damping force can be exerted from thebeginning of the switch in the extension/contraction direction withoutany delays in closing the extension-side leaf valve Ve and thecontraction-side leaf valve Vp.

Gaps may form between the annular plate 19 and the contraction-sidechamber 11 and between the annular plate 15 and the extension-sidechamber 12 due to deterioration over time of the valve body (annularplate 19) of the extension-side check valve Te and the valve body(annular plate 15) of the contraction-side check valve Tp, and this maylead to changes in the flow amount passing through the extension-sidepressure introduction passage Ie and the contraction-side pressureintroduction passage Ip. Since the extension-side resistance element andthe contraction-side resistance element are provided on the downstreamside of the extension-side pressure introduction passage Ie and thecontraction-side back pressure chamber Cp and on the downstream side ofthe contraction-side pressure introduction passage Ip and theextension-side back pressure chamber Ce, such changes in the flow amountdo not affect the damping force control or the valve-closing operationduring switching between extension/contraction.

On the outer peripheral side of the piston rod 7, the piston 2, theextension-side leaf valve Ve, the contraction-side leaf valve Vp, thecylindrical extension-side chamber 12, and the cylindricalcontraction-side chamber 11 are mounted. The piston 2 includes theextension-side passage 3 and the contraction-side passage 4, and theextension-side leaf valve Ve and the contraction-side leaf valve Vp arelaminated on the piston 2. The extension-side chamber 12 forms theextension-side back pressure chamber Ce, and the extension-side spool Seis slidingly inserted into the inner periphery of the extension-sidechamber 12. The contraction-side chamber 11 forms the contraction-sideback pressure chamber Cp, and the contraction-side spool Sp is slidinglyinserted into the inner periphery of the contraction-side chamber 11.The contraction-side pressure introduction passage Ip is provided to theextension-side chamber 12, and the extension-side pressure introductionpassage Ie is provided to the contraction-side chamber 11, and thus themembers required to adjust the damping force can be disposed in aconcentrated manner in the piston part of the shock absorber D1.

The extension-side leaf valve Ve of the extension-side spool Se and thevalve body (annular plate 15) of the contraction-side check valve Tpthat opens/closes the contraction-side pressure introduction passage Ipare biased by the single spring member 16. The contraction-side leafvalve Vp of the contraction-side spool Sp and the valve body (annularplate 19) of the extension-side check valve Te that opens/closes theextension-side pressure introduction passage Ie are biased by the singlespring member 20. Therefore, the check valves Te, Tp and the spools Se,Sp can be restored to the return side with the single spring members 16,20, and thus the number of parts can be reduced.

In the shock absorber D1, the retaining shaft 8 a, the vertical hole 8d, the extension-side pilot orifice Pe serving as the extension-sideresistance element, the contraction-side pilot orifice Pp serving as thecontraction-side resistance element, the accommodation part L, theadjustment passage Pc, and the contraction-side discharge passage Ep areprovided to the piston rod 7. The retaining shaft 8 a is provided on thedistal end of the piston rod 7, and the piston 2, the extension-sideleaf valve Ve, the contraction-side leaf valve Vp, the extension-sidechamber 12, and the contraction-side chamber 11 are mounted on the outerperiphery of the retaining shaft 8 a. The vertical hole 8 d opens fromthe distal end of the retaining shaft 8 a. The extension-side pilotorifice Pe and the contraction-side pilot orifice Pp are provided to theretaining shaft 8 a, and communicate with the communication passage 24provided in the vertical hole 8 d. The accommodation part L is providedon the inside of the piston rod 7 so as to communicate with the verticalhole 8 d, and the solenoid pressure control valve 6 is accommodated inthe accommodation part L. The adjustment passage Pc allows thecommunication passage 24 to communicate with the accommodation part L.The contraction-side discharge passage Ep allows the accommodation partL to communicate with the extension-side chamber R1. The shock absorberD1 includes the separator 23 that is inserted into the vertical hole 8d. The separator 23 forms, by the annular groove 23 a provided on theouter periphery thereof, the communication passage 24 that allows theextension-side back pressure chamber Ce to communicate with thecontraction-side back pressure chamber Cp within the vertical hole 8 d.The separator 23 also forms the extension-side discharge passage Ee onthe inner periphery thereof. Therefore, the solenoid pressure controlvalve 6 can be accommodated within the piston rod 7 without any trouble,and the extension-side back pressure chamber Ce and the contraction-sideback pressure chamber Cp can be provided on the outer periphery of thepiston rod 7 shifted in the axial direction from the solenoid pressurecontrol valve 6.

The solenoid pressure control valve 6 is set so as to close theadjustment passage Pc when not energized, and to perform pressurecontrol when energized. The shock absorber D1 includes the fail valve FVprovided in the adjustment passage Pc. The fail valve FV bypasses thesolenoid pressure control valve 6. The valve-opening pressure of thefail valve FV is greater than the maximum control pressure of thesolenoid pressure control valve 6. Thus, during a failure, theextension-side load and the contraction-side load reach a maximum, andthe shock absorber D1 exerts the greatest damping force. Therefore, thevehicle body posture can be stabilized even during a failure.

When the solenoid pressure control valve 6 enters the blocked position,the small-diameter part 31 a of the valve body 31 of the solenoid valveopposes the through hole 30 c to block the through hole 30 c, andthereby the solenoid pressure control valve 6 is closed. The solenoidpressure control valve 6 can also be made to function as a throttlevalve by not completely blocking the through hole 30 c and configuringthe recess 31 c so as to partially oppose the through hole 30 c in theblocked position or the like. Thereby, the characteristic of a throttlevalve achieved by the solenoid pressure control valve 6 when in theblocked position can be added to the damping characteristics,particularly the damping characteristics in a region in which the pistonspeed is low, of the shock absorber D1 during a failure. Thus, theriding comfort in the vehicle can be improved even during a failure.

The solenoid pressure control valve 6 includes: the cylindrical valveseat member 30; the small-diameter part 31 a; the large-diameter part 31b; the recess 31 c provided between the small-diameter part 31 a and thelarge-diameter part 31 b; and the valve body 31 of the solenoid valve.The valve seat member 30 includes the valve accommodation tube 30 a thatforms a portion of the adjustment passage Pc, and the annular valve seat30 d provided on the end of the valve accommodation tube 30 a. The valveaccommodation tube 30 a has the through hole 30 c that allows the insideto communicate with outside of the valve accommodation tube 30 a. Thesmall-diameter part 31 a is slidingly inserted into the valveaccommodation tube 30 a. The recess 31 c can oppose the through hole 30c. The valve body 31 of the solenoid valve makes the end of thelarge-diameter part 31 b separate from and sit on the valve seat 30 d ofthe control valve. The solenoid pressure control valve blocks theadjustment passage Pc by making the small-diameter part 31 a oppose thethrough hole 30 c. Thus, the pressure-receiving area on which pressurein a direction in which the valve body 31 of the solenoid valve escapesfrom the valve seat member 30 acts is an area obtained by subtractingthe area of a circle whose diameter is equal to the outer diameter ofthe small-diameter part 31 a from the area of a circle whose diameter isequal to the inner diameter of the valve seat 30 d of the control valve.Therefore, the pressure-receiving area can be greatly decreased, and theflow passage area during valve opening can be increased. Accordingly,the necessary solenoid thrust is small and the amount of movement of thevalve body 31 of the solenoid valve is also reduced, and thus themovement of the valve body 31 of the solenoid valve is stable. Further,in the blocked position, the outer periphery of the small-diameter part31 a opposes the through hole 30 c so that the through hole 30 c isblocked. Therefore, the solenoid pressure control valve 6 remains closedeven upon receiving pressure from the upstream side, and thus it ispossible to activate only the fail valve FV.

The above-described constitution of the biasing part is just oneexample, and the constitution of the biasing part is not limited to thatin the present embodiment. In the above, the present invention wasexplained using an example in which the present embodiment was realizedfor both the damping valve on the extension-side and the damping valveon the contraction-side. However, the present embodiment can also beapplied to only either one of the damping valve on the extension-side orthe damping valve on the contraction-side of the shock absorber.Although not illustrated, the present embodiment can also be applied toa damping valve provided to a base valve instead of a damping valveprovided to the piston part of a shock absorber.

Second Embodiment

As shown in FIG. 5 , a damping valve according to a second embodiment isutilized as both an extension-side damping valve and a contraction-sidedamping valve of a shock absorber D2. The damping valve includes thefollowing: a piston 2 serving as a valve disc; an extension-side firstleaf valve Ve1 serving as an annular first leaf valve; acontraction-side first leaf valve Vp1 serving as an annular first leafvalve; an extension-side second leaf valve Ve2 serving as an annularsecond leaf valve; a contraction-side first second valve Vp2 serving asan annular second leaf valve; and a biasing part that exerts a variablebiasing force on the extension-side second leaf valve Ve2 toward thepiston 2 side and exerts a variable biasing force on thecontraction-side second leaf valve Vp2 toward the piston 2 side. Thepiston 2 includes an extension-side passage 3 and a contraction-sidepassage 4 which serve as a passage, and an annular extension-side valveseat 2 d and an annular contraction-side valve seat 2 c thatrespectively surround the outlet ends of the extension-side passage 3and the contraction-side passage 4. The extension-side first leaf valveVe1 and the contraction-side first leaf valve Vp1 are laminated on thepiston 2. An extension-side first gap serving as a first gap is providedbetween the extension-side first leaf valve Ve1 and the extension-sidevalve seat 2 d. A contraction-side first gap serving as a first gap isprovided between the contraction-side first leaf valve Vp1 and thecontraction-side valve seat 2 c. The extension-side second leaf valveVe2 is laminated on the counter-valve disc side (counter-piston 2 side)of the extension-side first leaf valve Ve1. An extension-side second gapserving as a second gap is provided between the extension-side secondleaf valve Ve2 and the extension-side first leaf valve Ve1. Thecontraction-side second leaf valve Vp2 is laminated on the counter-valvedisc side (counter-piston 2 side) of the contraction-side first leafvalve Vp1. A contraction-side second gap serving as a second gap isprovided between the contraction-side second leaf valve Vp2 and thecontraction-side first leaf valve Vp1. The damping valve of the presentembodiment obviously may be applied to only the extension-side dampingvalve or to only the contraction-side damping valve of the shockabsorber D2.

Meanwhile, the shock absorber D2 includes the following: a cylinder 1;the above-described damping valve; an extension-side chamber R1 and acontraction-side chamber R2 that are partitioned within the cylinder 1by the piston 2; and a piston rod 7. When the piston 2 moves in theaxial direction (the up-down direction in FIG. 5 ) relative to thecylinder 1, the shock absorber D2 applies resistance with theextension-side first leaf valve Ve1 to the flow of liquid passingthrough the extension-side passage 3, and applies resistance with thecontraction-side first leaf valve Vp1 to the flow of liquid passingthrough the contraction-side passage 4, and thereby exerts a dampingforce.

Although not illustrated, a free piston is provided at the bottom inFIG. 5 of the cylinder 1 similar to the first embodiment. A gas chamberis formed within the cylinder 1 by the free piston. A seal (notillustrated) is provided between the piston rod 7 and the cylinder 1,and the inside of the cylinder 1 is in a liquid-tight state due to thisseal. As illustrated, the shock absorber D2 is set to a so-calledsingle-rod type. The volume of the piston rod 7 that moves into/out ofthe cylinder 1 according to the extension/contraction of the shockabsorber D2 is compensated by means of the volume of the gas within thegas chamber expanding or contracting and the free piston moving throughthe inside of the cylinder 1 in the up-down direction. In this way, theshock absorber D2 is set to a single-cylinder type. However, instead ofinstalling the free piston and the gas chamber, a reservoir may beprovided on the outer periphery or outside of the cylinder 1 and volumecompensation of the piston rod 7 may be performed by this reservoir.

In this embodiment, the biasing part of the damping valve includes thefollowing: an extension-side spool Se that biases the extension-sidesecond leaf valve Ve2; an extension-side back pressure chamber Ce thatpresses the extension-side spool Se with internal pressure; acontraction-side spool Sp that biases the contraction-side second leafvalve Vp2; a contraction-side back pressure chamber Cp that presses thecontraction-side spool Sp with internal pressure; a communicationpassage 24 that communicates with the extension-side back pressurechamber Ce via a contraction-side pilot orifice Pp serving as acontraction-side resistance element, and that communicates with thecontraction-side back pressure chamber Cp via an extension-side pilotorifice Pe serving as an extension-side resistance element; anextension-side pressure introduction passage Ie that permits only theflow of liquid from the extension-side chamber R1 toward thecontraction-side back pressure chamber Cp; a contraction-side pressureintroduction passage Ip that permits only the flow of liquid from thecontraction-side chamber R2 toward the extension-side back pressurechamber Ce; an adjustment passage Pc that is connected to thecommunication passage 24; a contraction-side discharge passage Ep thatallows the downstream of the adjustment passage Pc to communicate withthe extension-side chamber R1, and that permits only the flow of liquidfrom the adjustment passage Pc toward the extension-side chamber R1; anextension-side discharge passage Ee that allows the downstream of theadjustment passage Pc to communicate with the contraction-side chamberR2, and that permits only the flow of liquid from the adjustment passagePc toward the contraction-side chamber R2; and a solenoid pressurecontrol valve 6 provided in the adjustment passage Pc. Thecontraction-side pilot orifice Pp applies resistance to the flow ofliquid passing through the contraction-side pilot orifice Pp. Theextension-side pilot orifice Pe applies resistance to the flow of liquidpassing through the extension-side pilot orifice Pe. The solenoidpressure control valve 6 controls the upstream pressure of theadjustment passage Pc.

The damping valve and the shock absorber D2 will now be explained indetail. Those constitutions which are the same as in the firstembodiment will be assigned the same reference numeral, and explanationsthereof will be omitted.

As shown in FIG. 7 , the annular piston 2 is assembled onto the outerperiphery of the retaining shaft 8 a provided to the piston retainingmember 8. The following are assembled onto the outer periphery of theretaining shaft 8 a above the piston 2 in FIG. 7 : a contraction-sidefirst annular spacer 260 serving as a first annular spacer; thecontraction-side first leaf valve Vp1; a contraction-side second annularspacer 261 serving as a second annular spacer; the contraction-sidesecond leaf valve Vp2; a contraction-side spacer 262 serving as aspacer; a contraction-side annular plate 263 serving as an annularplate; a contraction-side plate stopper 264; the contraction-side spoolSp; and a contraction-side chamber 11. The contraction-side chamber 11forms the contraction-side back pressure chamber Cp. The following areassembled onto the outer periphery of the retaining shaft 8 a under thepiston 2 in FIG. 7 : an extension-side first annular spacer 265 servingas a first annular spacer; the extension-side first leaf valve Ve1; anextension-side second annular spacer 266 serving as a second annularspacer; the extension-side second leaf valve Ve2; an extension-sidespacer 267 serving as a spacer; an extension-side annular plate 268serving as an annular plate; an extension-side plate stopper 269; theextension-side spool Se; and an extension-side chamber 12. Theextension-side chamber 12 forms the extension-side back pressure chamberCe.

As shown in FIG. 7 , the extension-side first leaf valve Ve1 is formedin an annular shape so as to permit the insertion of the retaining shaft8 a of the piston retaining member 8. The inner periphery of theextension-side first leaf valve Ve1 is sandwiched by the piston 2 andthe extension-side chamber 12, and due to this sandwiching, theextension-side first leaf valve Ve1 is fixed to the retaining shaft 8 aof the piston retaining member 8. Deflection of the outer periphery ofthe extension-side first leaf valve Ve1 is permitted. In more detail,the extension-side second annular spacer 266, which has an outerdiameter than is smaller than the outer diameter of the extension-sidefirst leaf valve Ve, is interposed on the back surface side of theextension-side first leaf valve Ve1. Deflection of the extension-sidefirst leaf valve Ve1 toward the bottom side in FIG. 7 is permitted moretoward the outer periphery side from an area that is supported by theextension-side second annular spacer 266. Deflection of theextension-side first leaf valve Ve1 toward the top side in FIG. 7 ispermitted more toward an outer periphery side from an area that issupported by the extension-side first annular spacer 265.

The extension-side second leaf valve Ve2 is laminated on theextension-side second annular spacer 266 on the opposite side of thevalve disc (the bottom side in FIG. 7 ). Similar to the extension-sidefirst leaf valve Ve1, the inner periphery of the extension-side secondleaf valve Ve2 is sandwiched by the piston 2 and the extension-sidechamber 12, and due to this sandwiching, the extension-side second leafvalve Ve2 is fixed to the retaining shaft 8 a of the piston retainingmember 8. Deflection of the outer periphery of the extension-side secondleaf valve Ve2 is permitted. The extension-side second leaf valve Ve2 isdirectly sandwiched by the extension-side second annular spacer 266,which has an outer diameter that is smaller than the outer diameter ofthe extension-side second leaf valve Ve2, and the extension-side spacer267. Deflection of the extension-side second leaf valve Ve2 is permittedmore toward the outer periphery side from the area that is supported bythe extension-side second annular spacer 266 and the extension-sidespacer 267.

The extension-side first leaf valve Ve1 is laminated on the bottom inFIG. 7 of the piston 2 via the extension-side first annular spacer 265,which is laminated on the inner peripheral seat part 2 h of the piston2. In a state in which a load is not acting on the extension-side firstleaf valve Ve1, the extension-side first gap is formed between theextension-side first leaf valve Ve1 and the extension-side valve seat 2d. The length of the extension-side first gap in the up-down directionin FIG. 7 can be adjusted by exchanging for an extension-side firstannular spacer 265 of a different thickness or by changing the number ofextension-side first annular spacers 265 that are laminated. Theextension-side first gap between the extension-side first leaf valve Ve1and the extension-side valve seat 2 d can be formed without using theextension-side first annular spacer 265 by setting the height of theinner peripheral seat part 2 h to be greater than the height of theextension-side valve seat 2 d and directly laminating the extension-sidefirst leaf valve Ve1 onto the inner peripheral seat part 2 h. However,by providing the extension-side first annular spacer 265 to the innerperipheral seat part 2 h, the above-mentioned length of theextension-side first gap can be easily adjusted.

Further, the extension-side second leaf valve Ve2 is laminated on thebottom in FIG. 7 of the extension-side first leaf valve Ve1 via theextension-side second annular spacer 266. In a state in which a load isnot acting on the extension-side second leaf valve Ve2, theextension-side second gap is formed between the extension-side secondleaf valve Ve2 and the extension-side first leaf valve Ve1. The lengthof the extension-side second gap in the up-down direction in FIG. 7 canbe adjusted by exchanging for an extension-side second annular spacer266 of a different thickness or by changing the number of extension-sidesecond annular spacers 266 that are laminated. By providing theextension-side second annular spacer 266, the above-mentioned length ofthe extension-side second gap can be easily adjusted.

The extension-side annular plate 268 is slidably mounted on the outerperiphery of the extension-side spacer 267. The axial direction lengthof the extension-side annular plate 268 is shorter than the axialdirection length of the extension-side spacer 267. Thus, theextension-side annular plate 268 can move in the up-down direction whileslidingly contacting the outer periphery of the extension-side spacer267. Further, the annular extension-side plate stopper 269 is providedto the bottom in FIG. 7 of the extension-side spacer 267. The outerdiameter of the extension-side plate stopper 269 is set to be greaterthan the inner diameter of the extension-side annular plate 268. Theextension-side chamber 12 is laminated on the bottom of theextension-side plate stopper 269. The inner diameter of theextension-side annular plate 268 is set to be smaller than the outerdiameter of the inner peripheral seat part 2 h provided to the piston 2.The outer diameter of the extension-side annular plate 268 is set to begreater than the inner diameter of the extension-side valve seat 2 d.The extension-side annular plate 268 is configured such that it can movein the axial direction (the up-down direction in FIG. 7 ) between theextension-side second annular spacer 266 and the extension-side platestopper 269.

The extension-side annular plate 268 has a higher deflection rigiditythan that of the extension-side second leaf valve Ve2. In the presentembodiment, by setting the axial direction length (thickness) of theextension-side annular plate 268 to be greater than the axial directionlength (thickness) of the extension-side second leaf valve Ve2, therigidity of the extension-side annular plate 268 can be increased to begreater than the rigidity of the extension-side second leaf valve Ve2.Not only can the rigidity be strengthened by the thickness, but therigidity of the extension-side annular plate 268 can also be increasedby forming the extension-side annular plate 268 with a material having ahigher rigidity than that of the extension-side second leaf valve Ve2.

When the extension-side annular plate 268 is compressed from the backsurface side (opposite side of the piston 2) by the biasing part,specifically by the pressure within the extension-side back pressurechamber Ce and the extension-side spool Se, the extension-side annularplate 268 pushes up the extension-side second leaf valve Ve2 anddeflects together with the extension-side second leaf valve Ve2. Theextension-side second leaf valve Ve2 deflects as described above when abiasing force generated by the biasing part is loaded onto theextension-side second leaf valve Ve2 from the back surface side via theextension-side annular plate 268. If this biasing force increases andthe outer periphery displaces by an amount equal to or greater than theextension-side second gap, the extension-side second leaf valve Ve2abuts the extension-side first leaf valve Ve1. When the extension-sidesecond leaf valve Ve2 compresses the extension-side first leaf valveVe1, the extension-side first leaf valve Ve1 deflects. If thedisplacement of the outer periphery of the extension-side first leafvalve Ve1 caused by the deflection becomes equal to or greater than theextension-side first gap, the extension-side first leaf valve Ve1 sitson the extension-side valve seat 2 d and closes the extension-sidepassage 3.

When the extension-side first leaf valve Ve1 deflects to the point atwhich it sits on the extension-side valve seat 2 d, the extension-sideannular plate 268 enters a state in which it is supported by the innerperipheral seat part 2 h and the extension-side valve seat 2 d. In thisstate, the biasing force generated by the pressure within theextension-side back pressure chamber Ce and the extension-side spool Seis received by the extension-side annular plate 268. Thus, any furtherdeformation of the extension-side first leaf valve Ve1 and theextension-side second leaf valve Ve2 is suppressed, and an excessiveload is prevented from being applied to the extension-side first leafvalve Ve1 and the extension-side second leaf valve Ve2. Further, theextension-side annular plate 268 is slidably mounted on theextension-side spacer 267. Therefore, when the extension-side first leafvalve Ve1 and the extension-side second leaf valve Ve2 deflect in adirection away from the extension-side valve seat 2 d, theextension-side annular plate 268 moves downward in FIG. 7 relative tothe extension-side spacer 267. Thus, the deflection of theextension-side first leaf valve Ve1 and the extension-side second leafvalve Ve2 in the direction away from the piston 2 is not obstructed bythe extension-side annular plate 268.

The extension-side chamber 12 includes: an annular mounting part 12 athat is fitted onto the outer periphery of the retaining shaft 8 a ofthe piston retaining member 8; a flange 12 b that is provided on theouter periphery at the bottom end in FIG. 7 of the mounting part 12 a; asliding contact tube 12 c that extends from the outer periphery of theflange 12 b toward the piston 2 side; an annular groove 12 d provided onthe inner periphery of the mounting part 12 a; and a notch 12 e thatcommunicates with the annular groove 12 d from the outer periphery ofthe mounting part 12 a. In a state in which the extension-side chamber12 is assembled onto the retaining shaft 8 a, the annular groove 12 dopposes the contraction-side pilot orifice Pp provided to the retainingshaft 8 a. The extension-side plate stopper 269 is interposed betweenthe mounting part 12 a of the extension-side chamber 12 and theextension-side spacer 267. The extension-side plate stopper 269 may beeliminated and the lower limit of movement of the extension-side annularplate 268 may be restricted with the mounting part 12 a. There are casesin which it is necessary to adjust the position of the extension-sidechamber 12 so that it opposes the contraction-side pilot orifice Pp andthe annular groove 12 d when assembling the extension-side chamber 12onto the retaining shaft 8 a of the piston retaining member 8, and insuch cases, the extension-side plate stopper 269 is preferably providedbetween the mounting part 12 a and the extension-side spacer 267. Theposition of the extension-side chamber 12 relative to the pistonretaining member 8 can be adjusted by the extension-side plate stopper269.

The extension-side spool Se is accommodated within the sliding contacttube 12 c. The outer periphery of the extension-side spool Se slidinglycontacts the inner periphery of the sliding contact tube 12 c, and theextension-side spool Se is configured such that it can move in the axialdirection within the sliding contact tube 12 c. The extension-side spoolSe has an annular spool main body 13, and an annular projection 14 thatrises up from the inner periphery at the top end in FIG. 3 of the spoolmain body 13. The inner diameter of the annular projection 14 is set tobe smaller than the outer diameter of the extension-side annular plate268, and the annular projection 14 is configured such that it can abutthe back surface (bottom surface in FIG. 7 ) of the extension-sideannular plate 268.

When the extension-side spool Se is assembled to the extension-sidechamber 12 and the extension-side chamber 12 is assembled onto theretaining shaft 8 a, the extension-side back pressure chamber Ce isformed on the back surface side (the bottom side in FIG. 7 ) of theextension-side second leaf valve Ve2. The inner diameter of the spoolmain body 13 is greater than the outer diameter of the mounting part 12a. The inner diameter of the spool main body 13 can be set so that theinner periphery of the spool main body 13 slidingly contacts the outerperiphery of the mounting part 12 a, and the extension-side backpressure chamber Ce can be sealed by the extension-side spool Se.

The annular groove 12 d is provided on the inner periphery of themounting part 12 a of the extension-side chamber 12. The mounting part12 a includes the notch 12 e that communicates with the annular groove12 d from the outer periphery of the mounting part 12 a. In a state inwhich the extension-side chamber 12 is assembled onto the retainingshaft 8 a, the annular groove 12 d opposes the contraction-side pilotorifice Pp provided to the retaining shaft 8 a, and the extension-sideback pressure chamber Ce communicates with the contraction-side pilotorifice Pp.

Further, the contraction-side pressure introduction passage Ip thatopens from the outer periphery of the flange 12 b is provided to theextension-side chamber 12. The contraction-side chamber R2 communicateswith the inside of the extension-side back pressure chamber Ce via thecontraction-side pressure introduction passage Ip. An annular plate 15is laminated on the top end in FIG. 7 of the flange 12 b of theextension-side chamber 12. A spring member 16 is interposed between theannular plate 15 and the spool main body 13 of the extension-side spoolSe. The annular plate 15 is pressed toward the flange 12 b by the springmember 16 so that the contraction-side pressure introduction passage Ipis closed. The contraction-side pressure introduction passage Ip isconfigured so as to not generate any resistance against the flow ofpassing liquid.

If the shock absorber D2 contracts so that the contraction-side chamberR2 is compressed and the pressure therein increases, the annular plate15 is pressed by this pressure so that it separates from the flange 12b, and thereby the contraction-side pressure introduction passage Ip isopened. During extension of the shock absorber D2 in which the pressurewithin the extension-side back pressure chamber Ce increases higher thanthat of the contraction-side chamber R2, the annular plate 15 is pressedto the flange 12 b so as to close the contraction-side pressureintroduction passage Ip. In other words, the annular plate 15 functionsas a valve body of a contraction-side check valve Tp that permits onlythe flow of liquid from the contraction-side chamber R2. By thiscontraction-side check valve Tp, the contraction-side pressureintroduction passage Ip is set to a one-way passage that permits onlythe flow of liquid from the contraction-side chamber R2 toward theextension-side back pressure chamber Ce.

The spring member 16 functions to press the annular plate 15 to theflange 12 b. In other words, the spring member 16 constitutes thecontraction-side check valve Tp together with the valve body (theannular plate 15) of the check valve. The spring member 16 alsofunctions to bias the extension-side spool Se toward the extension-sidesecond leaf valve Ve2. When the extension-side second leaf valve Ve2deflects so that the extension-side spool Se is pushed down in thedirection away from the piston 2 (downwards in FIG. 7 ) and then thedeflection of the extension-side second leaf valve Ve2 subsequentlyterminates, the extension-side spool Se is still biased by the springmember 16, and thus the extension-side spool Se can quickly return toits original position (the position shown in FIG. 7 ) following theextension-side second leaf valve Ve2. It is also possible to bias theextension-side spool Se with a different spring member from the springmember 16. Using the same spring member for the spring member thatconstitutes the contraction-side check valve Tp and the spring memberthat biases the extension-side spool Se is advantageous because thenumber of parts can be reduced and the structure can be simplified. Theouter diameter of the extension-side spool Se is set to be greater thanthe inner diameter of the annular projection 14, and the annularprojection 14 is configured to abut the extension-side annular plate268. The extension-side spool Se is constantly biased toward theextension-side second leaf valve Ve2 by the pressure of theextension-side back pressure chamber Ce.

As shown in FIG. 7 , similar to the extension-side first leaf valve Ve1,the contraction-side first leaf valve Vp1 that is laminated on top ofthe piston 2 is formed in an annular shape so as to permit the insertionof the retaining shaft 8 a of the piston retaining member 8. The innerperiphery of the contraction-side first leaf valve Vp1 is sandwiched bythe piston 2 and the contraction-side chamber 11, and due to thissandwiching, the contraction-side first leaf valve Vp1 is fixed to theretaining shaft 8 a of the piston retaining member 8. Deflection of theouter periphery of the contraction-side first leaf valve Vp1 ispermitted. In more detail, the contraction-side second annular spacer261, which has an outer diameter that is larger than the outer diameterof the contraction-side first leaf valve Vp1, is interposed on the backsurface side of the contraction-side first leaf valve Vp1. Deflection ofthe contraction-side first leaf valve Vp1 toward the top side in FIG. 7is permitted more toward the outer periphery side from an area that issupported by the contraction-side second annular spacer 261. Deflectionof the contraction-side first leaf valve Vp1 toward the bottom side inFIG. 7 is permitted more toward an outer periphery side from an areathat is supported by the contraction-side first annular spacer 260.

The contraction-side second leaf valve Vp2 is laminated on thecontraction-side second annular spacer 261 on the opposite side of thevalve disc (the top side in FIG. 7 ). Similar to the contraction-sidefirst leaf valve Vp1, the inner periphery of the contraction-side secondleaf valve Vp2 is sandwiched by the piston 2 and the contraction-sidechamber 11, and due to this sandwiching, the contraction-side secondleaf valve Vp2 is fixed to the retaining shaft 8 a of the pistonretaining member 8. Deflection of the outer periphery of thecontraction-side second leaf valve Vp2 is permitted. Thecontraction-side second leaf valve Vp2 is directly sandwiched by thecontraction-side second annular spacer 261 and the contraction-sidespacer 262. The contraction-side second annular spacer 261 and thecontraction-side spacer 262 have outer diameters that are smaller thanthe outer diameter of the contraction-side second leaf valve Vp2.Deflection of the contraction-side second leaf valve Vp2 is permittedmore toward the outer periphery side from the area that is supported bythe contraction-side second annular spacer 261 and the contraction-sidespacer 262.

The contraction-side first leaf valve Vp1 is laminated on the top inFIG. 7 of the piston 2 via the contraction-side first annular spacer260, which is laminated on the inner peripheral seat part 2 f of thepiston 2. In a state in which a load is not acting on thecontraction-side first leaf valve Vp1, a contraction-side first gap isformed between the contraction-side first leaf valve Vp1 and thecontraction-side valve seat 2 c. The length of this gap in the up-downdirection in FIG. 7 can be adjusted by exchanging for a contraction-sidefirst annular spacer 260 of a different thickness or by changing thenumber of contraction-side first annular spacers 260 that are laminated.The contraction-side first gap between the contraction-side first leafvalve Vp1 and the contraction-side valve seat 2 c can be formed withoutusing the contraction-side first annular spacer 260 by setting theheight of the inner peripheral seat part 2 f to be greater than theheight of the contraction-side valve seat 2 c and directly laminatingthe contraction-side first leaf valve Vp1 onto the inner peripheral seatpart 2 f. However, by providing the contraction-side first annularspacer 260 to the inner peripheral seat part 2 f, the above-mentionedlength of the contraction-side first gap can be easily adjusted.

Further, the contraction-side second leaf valve Vp2 is laminated on thetop in FIG. 7 of the contraction-side first leaf valve Vp1 via thecontraction-side second annular spacer 261. In a state in which a loadis not acting on the contraction-side second leaf valve Vp2, thecontraction-side second gap is formed between the contraction-sidesecond leaf valve Vp2 and the contraction-side first leaf valve Vp1. Thelength of the contraction-side second gap in the up-down direction inFIG. 7 can be adjusted by exchanging for a contraction-side secondannular spacer 261 of a different thickness or by changing the number ofcontraction-side second annular spacers 261 that are laminated. Byproviding the contraction-side second annular spacer 261, theabove-mentioned length of the contraction-side second gap can be easilyadjusted.

The contraction-side annular plate 263 is slidably mounted on the outerperiphery of the contraction-side spacer 262. The axial direction lengthof the contraction-side annular plate 263 is shorter than the axialdirection length of the contraction-side spacer 262. Thus, thecontraction-side annular plate 263 can move in the up-down directionwhile slidingly contacting the outer periphery of the contraction-sidespacer 262. Further, the annular contraction-side plate stopper 264 isprovided to the top in FIG. 7 of the contraction-side spacer 262. Theouter diameter of the contraction-side plate stopper 264 is set to begreater than the inner diameter of the contraction-side annular plate263. The contraction-side chamber 11 is laminated on the top of thecontraction-side plate stopper 264. The inner diameter of thecontraction-side annular plate 263 is set to be smaller than the outerdiameter of the inner peripheral seat part 2 f provided to the piston 2.The outer diameter of the contraction-side annular plate 263 is set tobe greater than the inner diameter of the contraction-side valve seat 2c. The contraction-side annular plate 263 is configured such that it canmove in the axial direction (the up-down direction in FIG. 7 ) betweenthe contraction-side annular spacer 261 and the extension-side platestopper 264.

The contraction-side annular plate 263 has a higher deflection rigiditythan that of the contraction-side second leaf valve Vp2. In the presentembodiment, by setting the axial direction length (thickness) of thecontraction-side annular plate 263 to be greater than the axialdirection length (thickness) of the contraction-side second leaf valveVp2, the rigidity of the contraction-side annular plate 263 can beincreased to be greater than the rigidity of the contraction-side secondleaf valve Vp2. Not only can the rigidity be strengthened by thethickness, but the rigidity of the contraction-side annular plate 263can also be increased by forming the contraction-side annular plate 263with a material having a higher rigidity than that of thecontraction-side second leaf valve Vp2.

When the contraction-side annular plate 263 is compressed from the backsurface side (opposite side of the piston 2) by the biasing part,specifically by the pressure within the contraction-side back pressurechamber Cp and the contraction-side spool Sp, the contraction-sideannular plate 263 pushes down the contraction-side second leaf valve Vp2and deflects together with the contraction-side second leaf valve Vp2.The contraction-side second leaf valve Vp2 deflects as described abovewhen a biasing force generated by the biasing part is loaded onto thecontraction-side second leaf valve Vp2 from the back surface side viathe contraction-side annular plate 263. If this biasing force increasesand the outer periphery displaces by an amount equal to or greater thecontraction-side second gap, the contraction-side second leaf valve Vp2abuts the contraction-side first leaf valve Vp1. When thecontraction-side second leaf valve Vp2 compresses the contraction-sidefirst leaf valve Vp1, the contraction-side first leaf valve Vp1deflects. If the displacement of the outer periphery of thecontraction-side first leaf valve Vp1 caused by the deflection becomesequal to or greater than the contraction-side first gap, thecontraction-side first leaf valve Vp1 sits on the contraction-side valveseat 2 c and closes the contraction-side passage 4.

When the contraction-side first leaf valve Vp1 deflects to the point atwhich it sits on the contraction-side valve seat 2 c, thecontraction-side annular plate 263 enters a state in which it issupported by the inner peripheral seat part 2 f and the contraction-sidevalve seat 2 c. In this state, the biasing force generated by thepressure within the contraction-side back pressure chamber Cp and thecontraction-side spool Sp is received by the contraction-side annularplate 263. Thus, any further deformation of the contraction-side firstleaf valve Vp1 and the contraction-side second leaf valve Vp2 issuppressed, and an excessive load is prevented from being applied to thecontraction-side first leaf valve Vp1 and the contraction-side secondleaf valve Vp2. Further, the contraction-side annular plate 263 isslidably mounted on the contraction-side spacer 262. Therefore, when thecontraction-side first leaf valve Vp1 and the contraction-side secondleaf valve Vp2 deflect in a direction away from the contraction-sidevalve seat 2 c, the contraction-side annular plate 263 moves upward inFIG. 7 relative to the contraction-side spacer 262. Thus, the deflectionof the contraction-side first leaf valve Vp1 and the contraction-sidesecond leaf valve Vp2 in the direction away from the piston 2 is notobstructed by the contraction-side annular plate 263.

The contraction-side chamber 11 includes: an annular mounting part 11 athat is fitted onto the outer periphery of the retaining shaft 8 a ofthe piston retaining member 8; a flange 11 b that is provided on theouter periphery at the top end in FIG. 7 of the mounting part 11 a; asliding contact tube 11 c that extends from the outer periphery of theflange 11 b toward the piston 2 side; an annular groove 11 d provided onthe inner periphery of the mounting part 11 a; and a notch 11 e thatcommunicates with the annular groove 11 d from the outer periphery ofthe mounting part 11 a. In a state in which the contraction-side chamber11 is assembled onto the retaining shaft 8 a, the annular groove 11 dopposes the extension-side pilot orifice Pe provided to the retainingshaft 8 a. The contraction-side plate stopper 264 is interposed betweenthe mounting part 11 a of the contraction-side chamber 11 and thecontraction-side spacer 262. The contraction-side plate stopper 264 maybe eliminated and the upper limit of movement of the contraction-sideannular plate 263 may be restricted with the mounting part 11 a. Thereare cases in which it is necessary to adjust the position of thecontraction-side chamber 11 so that it opposes the extension-side pilotorifice Pe and the annular groove 11 d when assembling thecontraction-side chamber 11 onto the retaining shaft 8 a of the pistonretaining member 8, and in such cases, the contraction-side platestopper 264 is preferably provided between the mounting part 11 a andthe contraction-side spacer 262. The position of the contraction-sidechamber 11 relative to the piston retaining member 8 can be adjusted bythe contraction-side plate stopper 264.

The contraction-side spool Sp is accommodated within the sliding contacttube 11 c. The outer periphery of the contraction-side spool Spslidingly contacts the inner periphery of the sliding contact tube 11 c,and the contraction-side spool Sp is configured such that it can move inthe axial direction within the sliding contact tube 11 c. Thecontraction-side spool Sp has an annular spool main body 17, and anannular projection 18 that rises up from the outer periphery at thebottom end in FIG. 7 of the spool main body 17. The inner diameter ofthe annular projection 18 is set to be smaller than the outer diameterof the contraction-side annular plate 263, and the annular projection 18is configured such that it can abut the back surface (top surface inFIG. 7 ) of the contraction-side annular plate 263.

When the contraction-side spool Sp is assembled to the contraction-sidechamber 11 and the contraction-side chamber 11 is assembled onto theretaining shaft 8 a, the contraction-side back pressure chamber Cp isformed on the back surface side (the top side in FIG. 7 ) of thecontraction-side second leaf valve Vp2. The inner diameter of the spoolmain body 17 is greater than the outer diameter of the mounting part 11a. The inner diameter of the spool main body 17 can be set so that theinner periphery of the spool main body 17 slidingly contacts the outerperiphery of the mounting part 11 a, and the contraction-side backpressure chamber Cp can be sealed by the contraction-side spool Sp.

The annular groove 11 d is provided on the inner periphery of themounting part 11 a of the contraction-side chamber 11. The mounting part11 a includes the notch 11 e that communicates with the annular groove11 d from the outer periphery of the mounting part 11 a. In a state inwhich the contraction-side chamber 11 is assembled onto the retainingshaft 8 a, the annular groove 11 d opposes the extension-side pilotorifice Pe provided to the retaining shaft 8 a, and the contraction-sideback pressure chamber Cp communicates with the extension-side pilotorifice Pe. By communicating with the extension-side pilot orifice Pe,the contraction-side back pressure chamber Cp is also in communicationwith the extension-side back pressure chamber Ce through the connectionpassage 24 formed within the vertical hole 8 d of the retaining shaft 8a and the contraction-side pilot orifice Pp.

Further, the extension-side pressure introduction passage Ie that opensfrom the outer periphery of the flange 11 b is provided to thecontraction-side chamber 11. The extension-side chamber R1 communicateswith the inside of the contraction-side back pressure chamber Cp via theextension-side pressure introduction passage Ie. An annular plate 19 islaminated on the bottom end in FIG. 7 of the flange 11 b of thecontraction-side chamber 11. A spring member 20 is interposed betweenthe annular plate 19 and the spool main body 17 of the contraction-sidespool Sp. The annular plate 19 is pressed toward the flange 11 b by thespring member 20 so that the extension-side pressure introductionpassage Ie is closed. The extension-side pressure introduction passageIe is configured so as to not generate any resistance against the flowof passing liquid.

If the shock absorber D2 extends so that the extension-side chamber R1is compressed and the pressure therein increases, the annular plate 19is pressed by this pressure so that it separates from the flange 11 b,and thereby the extension-side pressure introduction passage Ie isopened. During contraction of the shock absorber D2 in which thepressure within the contraction-side back pressure chamber Cp increaseshigher than that of the extension-side chamber R1, the annular plate 19is pressed to the flange 11 b so as to close the extension-side pressureintroduction passage Ie. In other words, the annular plate 19 functionsas a valve body of an extension-side check valve Te that permits onlythe flow of liquid from the extension-side chamber R1. By thisextension-side check valve Te, the extension-side pressure introductionpassage Ie is set to a one-way passage that permits only the flow ofliquid from the extension-side chamber R1 toward the contraction-sideback pressure chamber Cp.

As explained above, the connection passage 24 is in communication withthe inside of the accommodation part L through the annular groove 8 e,the port 8 f, and the horizontal hole 8 g provided to the pistonretaining member 8. Thus, not only are the extension-side back pressurechamber Ce and the contraction-side back pressure chamber Cp incommunication with each other via the extension-side pilot orifice Pe,the contraction-side pilot orifice Pp, and the communication passage 24,but the extension-side back pressure chamber Ce and the contraction-sideback pressure chamber Cp are also in communication with theextension-side chamber R1 via the extension-side pressure introductionpassage Ie, and in communication with the contraction-side chamber R2via the contraction-side pressure introduction passage Ip, and are alsoin communication with the accommodation part L by means of the port 8 fand the horizontal hole 8 g.

The spring member 20 functions to press the annular plate 19 to theflange 11 b. In other words, the spring member 20 constitutes theextension-side check valve Te together with the valve body (annularplate 19) of the check valve. The spring member 20 also functions tobias the contraction-side spool Sp toward the contraction-side secondleaf valve Vp2. When the contraction-side second leaf valve Vp2 deflectsso that the contraction-side spool Sp is pushed up in the direction awayfrom the piston 2 (upwards in FIG. 7 ) and then the deflection of thecontraction-side second leaf valve Vp2 subsequently terminates, thecontraction-side spool Sp is still biased by the spring member 20, andthus the contraction-side spool Sp can quickly return to its originalposition (the position shown in FIG. 7 ) following the contraction-sidesecond leaf valve Vp2. It is also possible to bias the contraction-sidespool Sp with a different spring member from the spring member 20. Usingthe same spring member for the spring member that constitutes theextension-side check valve Te and the spring member that biases thecontraction-side spool Sp is advantageous because the number of partscan be reduced and the structure can be simplified. The outer diameterof the contraction-side spool Sp is set to be greater than the innerdiameter of the annular projection 18, and the annular projection 18 isconfigured to abut the contraction-side annular plate 263. Thecontraction-side spool Sp is constantly biased toward thecontraction-side second leaf valve Vp2 by the pressure of thecontraction-side back pressure chamber Cp. Therefore, a spring memberfor the purpose of biasing only the contraction-side spool Sp does nothave to be provided to the shock absorber D2.

The extension-side spool Se receives the pressure of the extension-sideback pressure chamber Ce and biases the extension-side second leaf valveVe2 toward the piston 2 via the extension-side annular plate 268. In astate in which the extension-side second leaf valve Ve2 abuts theextension-side first leaf valve Ve1, the extension-side spool Se alsobiases the extension-side first leaf valve Ve1 toward the piston 2. Thepressure-receiving area of the extension-side spool Se that receives thepressure of the extension-side back pressure chamber Ce is thedifference obtained by subtracting the area of a circle whose diameteris equal to the inner diameter of the annular projection 14 from thearea of a circle whose diameter is equal to the outer diameter of theextension-side spool Se.

Similarly, the contraction-side spool Sp receives the pressure of thecontraction-side back pressure chamber Cp and biases thecontraction-side second leaf valve Vp2 toward the piston 2 via thecontraction-side annular plate 263. In a state in which thecontraction-side second leaf valve Vp2 abuts the contraction-side firstleaf valve Vp1, the contraction-side spool Sp also biases thecontraction-side first leaf valve Vp1 toward the piston 2. Thepressure-receiving area of the contraction-side spool Sp that receivesthe pressure of the contraction-side back pressure chamber Cp is thedifference obtained by subtracting the area of a circle whose diameteris equal to the inner diameter of the annular projection 18 from thearea of a circle whose diameter is equal to the outer diameter of thecontraction-side spool Sp. In the hydraulic shock absorber D2 of thepresent embodiment, the pressure-receiving area of the extension-sidespool Se is greater than the pressure-receiving area of thecontraction-side spool Sp.

The annular projection 14 of the extension-side spool Se abuts the backsurface of the extension-side annular plate 268, and the extension-sideannular plate 268 is mounted on the outer periphery of theextension-side spacer 267. The pressure-receiving area in which thepressure of the extension-side back pressure chamber Ce directly acts onthe extension-side annular plate 268 is obtained by subtracting the areaof a circle whose diameter is equal to the outer diameter of theextension-side spacer 267 from the area of a circle whose diameter isequal to the inner diameter of the annular projection 14. Therefore, thesize of the extension-side load is obtained by multiplying the pressureof the extension-side back pressure chamber Ce by an area obtained bysubtracting the area of a circle whose diameter is equal to the outerdiameter of the extension-side spacer 267 from the area of a circlewhose diameter is equal to the outer diameter of the extension-sidespool Se. The extension-side second leaf valve Ve2 and theextension-side first leaf valve Ve1 are biased toward the piston 2 bythe extension-side load. The extension-side annular plate 268 may beeliminated and the annular projection 14 may be directly abutted to theback surface of the extension-side second leaf valve Ve2.

The annular projection 18 of the contraction-side spool Sp abuts theback surface of the contraction-side annular plate 263, and thecontraction-side annular plate 263 is mounted on the outer periphery ofthe contraction-side spacer 262. The pressure-receiving area in whichthe pressure of the contraction-side back pressure chamber Cp directlyacts on the contraction-side annular plate 263 is obtained bysubtracting the area of a circle whose diameter is equal to the outerdiameter of the contraction-side spacer 262 from the area of a circlewhose diameter is equal to the inner diameter of the annular projection18. Therefore, the size of the contraction-side load is obtained bymultiplying the pressure of the contraction-side back pressure chamberCp by an area obtained by subtracting the area of a circle whosediameter is equal to the outer diameter of the contraction-side spacer262 from the area of a circle whose diameter is equal to the outerdiameter of the contraction-side spool Sp. The contraction-side secondleaf valve Vp2 and the contraction-side first leaf valve Ve1 are biasedtoward the piston 2 by the contraction-side load. The contraction-sideannular plate 263 may be eliminated and the annular projection 18 may bedirectly abutted to the back surface of the contraction-side second leafvalve Vp2.

In this way, the shock absorber D2 is set such that when the pressure ofthe extension-side back pressure chamber Ce and the pressure of thecontraction-side back pressure chamber Cp are the same, the loadreceived by the extension-side second leaf valve Ve2 from theextension-side back pressure chamber Ce (extension-side load) is greaterthan the load received by the contraction-side second leaf valve Vp2from the contraction-side back pressure chamber Cp (contraction-sideload). Further, the shock absorber D2 is set such that in a state inwhich the pressure of the extension-side back pressure chamber Ce andthe pressure of the contraction-side back pressure chamber Cp are thesame and the extension-side second leaf valve Ve2 abuts theextension-side first leaf valve Ve1 and the contraction-side second leafvalve Vp2 abuts the contraction-side first leaf valve Vp1, the loadreceived by the extension-side second leaf valve Ve2 and theextension-side first leaf valve Ve1 from the extension-side backpressure chamber Ce (extension-side load) is greater than the loadreceived by the contraction-side second leaf valve Vp2 and thecontraction-side first leaf valve Vp1 from the contraction-side backpressure chamber Cp (contraction-side load).

In the case that the extension-side back pressure chamber Ce is closedby the extension-side spool Se and the pressure of the extension-sideback pressure chamber Ce does not directly act on the extension-sideannular plate 268, the extension-side load is determined by only thepressure-receiving area of the extension-side spool Se that receives thepressure of the extension-side back pressure chamber Ce. Similarly, inthe case that the contraction-side back pressure chamber Cp is closed bythe contraction-side spool Sp and the pressure of the contraction-sideback pressure chamber Cp does not directly act on the contraction-sideannular plate 263, the contraction-side load is determined by only thepressure-receiving area of the contraction-side spool Sp that receivesthe pressure of the contraction-side back pressure chamber Cp.Therefore, in an embodiment in which the pressures from the backpressure chambers Ce, Cp do not act directly on the extension-sideannular plate 268 and the contraction-side annular plate 263, in orderto set the shock absorber D2 such that the extension-side load receivedby the extension-side first leaf valve Ve1 and the extension-side secondleaf valve Ve2 from the extension-side back pressure chamber Ce isgreater than the contraction-side load received by the contraction-sidesecond leaf valve Vp2 or by the contraction-side first leaf valve Vp1and the contraction-side second leaf valve Vp2 from the contraction-sideback pressure chamber Cp when the pressure of the extension-side backpressure chamber Ce and the pressure of the contraction-side backpressure chamber Cp are the same, it is sufficient to set thepressure-receiving area of the extension-side spool Se to be greaterthan the pressure-receiving area of the contraction-side spool Sp.

In the case that the extension-side annular plate 268 and thecontraction-side plate 263 are eliminated, the pressure of theextension-side back pressure chamber Ce can be made to act directly onthe extension-side second leaf valve Ve2, and the pressure of thecontraction-side back pressure chamber Cp can be made to act directly onthe contraction-side second leaf valve Vp2. Further, in a structure inwhich the extension-side back pressure chamber Ce is closed by theextension-side spool Se, the extension-side spool Se can be abutted tothe extension-side second leaf valve Ve2, and in a structure in whichthe contraction-side back pressure chamber Cp is closed by thecontraction-side spool Sp, the contraction-side spool Sp can be abuttedto the contraction-side second leaf valve Vp2. Whether or not to closethe extension-side back pressure chamber Ce and the contraction-sideback pressure chamber Cp with the spools is a matter that can bearbitrarily selected.

In the present embodiment, since the extension-side spool Se and thecontraction-side spool Sp are used, the pressure-receiving area in whichthe pressure of the extension-side back pressure chamber Cesubstantially acts on the extension-side second leaf valve Ve2 can beset to be greater than the pressure-receiving area of only theextension-side second leaf valve Ve2. Since the difference between thepressure-receiving areas of the contraction-side spool Sp and theextension-side spool Se can be increased, the difference between theextension-side load and the contraction-side load can be increased.Thus, an extremely high degree of freedom can be imparted to the settingwidths of the extension-side load and the contraction-side load.

If the extension-side second leaf valve Ve2 is made to deflect by theextension-side load so as to abut the extension-side first leaf valveVe1, and the extension-side first leaf valve Ve1 is made to deflect tothe point at which it abuts the extension-side valve seat 2 d, theextension-side first leaf valve Ve1 closes extension-side passage 3. Theextension-side load acting on the extension-side first leaf valve Ve1during at a certain piston speed can be set by the above-mentionedpressure-receiving area, the deflection rigidity of the extension-sidefirst leaf valve Ve1 and the extension-side second leaf valve Ve2, etc.In other words, by setting the above-mentioned pressure-receiving area,the deflection rigidity of the extension-side first leaf valve Ve1 andthe extension-side second leaf valve Ve2, etc., the extension-sidepassage 3 can be closed by the extension-side first leaf valve Ve1 at acertain piston speed.

Similar to the extension-side first leaf valve Ve1, the contraction-sidefirst leaf valve Vp1 deflects due to the contraction-side load and abutsthe contraction-side valve seat 2 c so as to close the contraction-sidepassage 4. The contraction-side load acting on the contraction-sidefirst leaf valve Vp1 at a certain piston speed can be set by theabove-mentioned pressure-receiving area, the deflection rigidity of thecontraction-side first leaf valve Vp1 and the contraction-side secondleaf valve Vp2, etc. In other words, by setting the above-mentionedpressure-receiving area, the deflection rigidity of the contraction-sidefirst leaf valve Vp1 and the contraction-side second leaf valve Vp2,etc., the contraction-side passage 4 can be closed by thecontraction-side first leaf valve Vp1 at a certain piston speed.

As shown in FIG. 5 , the extension-side back pressure chamber Ce and thecontraction-side back pressure chamber Cp are on the upstream side andthe extension-side discharge passage Ee and the contraction-sidedischarge passage Ep are on the downstream side, and these are incommunication with each other via the adjustment passage Pc. Thesolenoid pressure control valve 6 is provided in the adjustment passagePc so that the pressures of the upstream extension-side back pressurechamber Ce and the contraction-side back pressure chamber C can becontrolled. Since the extension-side load is greater than thecontraction-side load, when controlling the pressures within theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp by the solenoid pressure control valve 6, theextension-side load can be increased with even a small pressure. If theextension-side damping force is increased, the maximum pressure to becontrolled by the solenoid pressure control valve 6 can be decreased.

In the present embodiment, the inner periphery of the extension-sidespool Se does not slidingly contact the outer periphery of the mountingpart 12 a of the extension-side chamber 12. The pressure of theextension-side back pressure chamber Ce also acts on the inside of theabutting site of the annular projection 14 on the back surface side ofthe extension-side annular plate 268 so as to bias the extension-sidesecond leaf valve Ve2. In setting the extension-side load, the settingshould be made considering the load that directly biases theextension-side second leaf valve Ve2 with the pressure of theextension-side back pressure chamber Ce.

Similarly, the inner periphery of the contraction-side spool Sp does notslidingly contact the outer periphery of the mounting part 11 a of thecontraction-side chamber 11. The pressure of the contraction-side backpressure chamber Cp also acts on the inside of the abutting site of theannular projection 18 on the back surface side of the contraction-sideannular plate 263 so as to bias the contraction-side second leaf valveVp2. In setting the contraction-side load, the setting should be madeconsidering the load that directly biases the contraction-side secondleaf valve Vp2 with the pressure of the contraction-side back pressurechamber Cp.

In the present embodiment, the solenoid pressure control valve 6 is setso as to close the adjustment passage Pc when not energized, and toperform pressure control when energized. A fail valve FV that bypassesthe solenoid pressure control valve 6 is provided in the adjustmentpassage Pc. The structure of the solenoid pressure control valve 6 andthe structure of the fail valve FV are basically the same as those inthe first embodiment, and thus explanations thereof will be omittedherein.

Next, the operation of the shock absorber D2 will be explained.

First, a case in which the damping force characteristics of the shockabsorber D2 are set to soft, i.e. a case in which the biasing force thatis generated by the biasing part and biases the extension-side secondleaf valve Ve2 and the contraction-side second leaf valve Vp2 isdecreased and the damping coefficient is decreased, will be explained.In order to make the damping force characteristics soft, the biasingforce that is applied to the extension-side second leaf valve Ve2 andthe contraction-side second leaf valve Vp2 by the biasing part isdecreased. Specifically, the resistance applied by the solenoid pressurecontrol valve 6 to the passing liquid is decreased by energizing thesolenoid Sol.

More specifically, the biasing force is controlled to form theextension-side first gap between the extension-side first leaf valve Ve1and the extension-side valve seat 2 d so that the extension-side secondleaf valve Ve2 does not abut the extension-side first leaf valve Ve1even if the extension-side second leaf valve Ve2 is made to deflect bythe biasing force generated by the biasing part, or so that theextension-side first leaf valve Ve1 does not sit on the extension-sidevalve seat 2 d even if the extension-side second valve leaf Ve2 abutsthe extension-side first leaf valve Ve1. Similarly, the biasing force iscontrolled to form the contraction-side first gap between thecontraction-side first leaf valve Vp1 and the contraction-side valveseat 2 c so that the contraction-side second leaf valve Vp2 does notabut the contraction-side first leaf valve Vp1 even if thecontraction-side second leaf valve Vp2 is made to deflect by the biasingforce generated by the biasing part, or so that the contraction-sidefirst leaf valve Vp1 does not sit on the contraction-side valve seat 2 ceven if the contraction-side second valve leaf Vp2 abuts thecontraction-side first leaf valve Vp1.

In this state, if the shock absorber D2 extends and the piston 2 movesupward in FIG. 5 , the liquid within the extension-side chamber R1 thatis compressed pushes the extension-side first leaf valve Ve1 causing itto deflect. The liquid within the extension-side chamber R1 passesthrough the extension-side passage 3 and moves to the contraction-sidechamber R2 that is expanded. Since the extension-side first gap isformed between the extension-side first leaf valve Ve1 and theextension-side valve seat 2 d, the liquid passes through theextension-side first gap. The flow path area of the extension-side firstgap is greater than the flow path area in a state in which the leafvalve is made to sit on the valve seat in a conventional shock absorber(for example, the flow path area of a notch provided to the leaf valveor an orifice provided to the valve seat by punching). Therefore, asindicated by the line B2 in FIG. 8 , the shock absorber D2 can reducethe damping force when the piston speed is in a low-speed regioncompared to the damping force generated by a conventional shock absorberas shown by the line A2.

When the pressure within the extension-side chamber R1 rises inaccordance with the extension of the shock absorber D2, theextension-side first leaf valve Ve1 deflects. The amount of thisdeflection is determined by the balance between a force that isgenerated by the pressure of the extension-side chamber R1 and thatattempts to make the extension-side first leaf valve Ve1 deflect fromthe extension-side passage 3 side, and a force that is generated by thespring reaction force possessed by the extension-side first leaf valveVe1 itself according to the above-mentioned amount of deflection andthat attempts to return the extension-side first leaf valve Ve1 to theextension-side valve seat 2 d side. The extension-side first leaf valveVe1 opens the extension-side passage 3 by deflecting.

If the shock absorber D2 extends at a high piston speed, the pressurewithin the extension-side chamber R1 increases and the extension-sidefirst leaf valve Ve1 deflects greatly. If the outer periphery of theextension-side first leave valve Ve1 displaces by an amount equal to orgreater than the extension-side second gap, it abuts the extension-sidesecond leaf valve Ve2 and thus the deflection of the extension-sidefirst leaf valve Ve1 is suppressed. Therefore, the inclination of thedamping force characteristics of the shock absorber D2 graduallyincreases together with an increase in the piston speed as indicated bythe line B2 in FIG. 8 .

If the shock absorber D2 extends at an even higher piston speed, thepressure within the extension-side chamber R1 increases further, and theforce causing the extension-side first leaf valve Ve1 to deflect alsoincreases. If the force causing the extension-side first leaf valve Ve1to deflect surpasses the force generated by the extension-side backpressure chamber Ce that pushes down the extension-side second leafvalve Ve2, the extension-side second leaf valve Ve2 deflects togetherwith the extension-side first leaf valve Ve1 in a direction away fromthe piston 2. As a result, the extension-side first gap between theextension-side valve seat 2 d and the extension-side first leaf valveVe1 increases. The inclination of the damping force characteristics ofthe shock absorber D2 begins to decrease part way through as indicatedby the line B2 in FIG. 8 .

The liquid within the extension-side chamber R1 pushes and opens theextension-side check valve Te, and passes through the extension-sidepressure introduction passage Ie and flows to the adjustment passage Pc.The liquid that has passed through the adjustment passage Pc pushes andopens the check valve 25, and is discharged to the contraction-sidechamber R2 on the low-pressure side via the extension-side dischargepassage Ee. The extension-side pilot orifice Pe applies resistance whenliquid passes therethrough to cause a pressure loss. In a state in whichthe liquid is flowing, the pressure downstream of the adjustment passagePc decreases lower than the pressure of the extension-side chamber R1,and thus the check valve 22 provided to the contraction-side dischargepassage Ep does not open and remains closed.

The extension-side pressure introduction passage Ie not onlycommunicates with the contraction-side back pressure chamber Cp, butalso communicates with the extension-side back pressure chamber Ce viathe communication passage 24. Since the contraction-side pressureintroduction passage Ip is closed by the contraction-side check valveTp, during extension of the shock absorber D2, the pressure within theextension-side back pressure chamber Ce can be increased higher thanthat of the contraction-side chamber R2. The pressure of thecontraction-side back pressure chamber Cp becomes higher than thepressure of the contraction-side chamber R2 on the low-pressure side,and biases the contraction-side second leaf valve Vp2 that closes thecontraction-side passage 4. Since a flow of liquid is not generated inthe contraction-side passage 4, there is no problem even if thecontraction-side second leaf valve Vp2 closes the contraction-sidepassage 4.

The solenoid pressure control valve 6 is provided in the adjustmentpassage Pc as explained above. When the solenoid Sol of the solenoidpressure control valve 6 is energized so as to control the pressure onthe upstream side of the adjustment passage Pc, the pressure within theextension-side back pressure chamber Ce can be adjusted and theextension-side load can be controlled to a desired load. Given theabove, the extension-side load that compresses the extension-side secondleaf valve Ve2 can be controlled by the solenoid pressure control valve6. By controlling the extension-side load, the gap amount of theextension-side first gap between the extension-side first leaf valve Ve1and the extension-side valve seat 2 d (the opening degree of theextension-side first leaf valve Ve1) in a state in which theextension-side first leaf valve Ve1 abuts the extension-side second leafvalve Ve2 can be controlled. Thereby, the extension-side damping forceduring extension of the shock absorber D2 can be controlled.

If the shock absorber D2 contracts and the piston 2 moves downward inFIG. 5 , the liquid within the contraction-side chamber R2 that iscompressed pushes the contraction-side first leaf valve Vp1 causing itto deflect. The liquid within the contraction-side chamber R2 passesthrough the contraction-side passage 4 and moves to the extension-sidechamber R1 that is expanded. Since the contraction-side first gap isformed between the contraction-side first leaf valve Vp1 and thecontraction-side valve seat 2 c, the liquid passes through thecontraction-side first gap. The flow path area of the contraction-sidefirst gap is greater than the flow path area in a state in which theleaf valve is made to sit on the valve seat in a conventional shockabsorber (for example, the flow path area of a notch provided to theleaf valve or an orifice provided to the valve seat by punching).Therefore, as indicated by the line D2 in FIG. 8 , the shock absorber D2can reduce the damping force when the piston speed is in a low-speedregion compared to the damping force generated by a conventional shockabsorber as shown by the line C2.

When the pressure within the contraction-side chamber R2 rises inaccordance with the contraction of the shock absorber D2, thecontraction-side first leaf valve Vp1 deflects. The amount of thisdeflection is determined by the balance between a force that isgenerated by the pressure of the contraction-side chamber R2 and thatattempts to make the contraction-side first leaf valve Vp1 deflect fromthe contraction-side passage 4 side, and a force that is generated bythe spring reaction force possessed by the contraction-side first leafvalve Vp1 itself according to the above-mentioned amount of deflectionand that attempts to return the contraction-side first leaf valve Vp1 tothe contraction-side valve seat 2 c side. The contraction-side firstleaf valve Vp1 opens the contraction-side passage 4 by deflecting.

If the shock absorber D2 extends at a high piston speed, the pressurewithin the contraction-side chamber R2 increases and thecontraction-side first leaf valve Vp1 deflects greatly. If the outerperiphery of the contraction-side first leave valve Ve2 displaces by anamount equal to or greater than the contraction-side second gap, itabuts the contraction-side second leaf valve Vp2 and thus the deflectionof the contraction-side first leaf valve Vp1 is suppressed. Therefore,the inclination of the damping force characteristics of the shockabsorber D2 gradually increases together with an increase in the pistonspeed as indicated by the line D2 in FIG. 8 .

If the shock absorber D2 extends at an even higher piston speed, thepressure within the contraction-side chamber R2 increases further, andthe force causing the contraction-side first leaf valve Vp1 to deflectalso increases. If the force causing the contraction-side first leafvalve Vp1 to deflect surpasses the force generated by thecontraction-side back pressure chamber Cp that pushes down thecontraction-side second leaf valve Vp2, the contraction-side second leafvalve Vp2 deflects together with the contraction-side first leaf valveVp1 in a direction away from the piston 2. As a result, thecontraction-side first gap between the contraction-side valve seat 2 cand the contraction-side first leaf valve Vp1 increases. The inclinationof the damping force characteristics of the shock absorber D2 begins todecrease part way through as indicated by the line D2 in FIG. 8 .

The liquid within the contraction-side chamber R2 pushes and opens thecontraction-side check valve Tp, and passes through the contraction-sidepressure introduction passage Ip and flows to the adjustment passage Pc.The liquid that has passed through the adjustment passage Pc pushes andopens the check valve 22, and is discharged to the extension-sidechamber R1 on the low-pressure side via the contraction-side dischargepassage Ep. The contraction-side pilot orifice Pp applies resistancewhen liquid passes therethrough to cause a pressure loss. In a state inwhich the liquid is flowing, the pressure downstream of the adjustmentpassage Pc decreases lower than the pressure of the contraction-sidechamber R2, and thus the check valve 25 provided to the extension-sidedischarge passage Ee does not open and remains closed.

The contraction-side pressure introduction passage Ip not onlycommunicates with the extension-side back pressure chamber Ce, but alsocommunicates with the contraction-side back pressure chamber Cp via thecommunication passage 24. Since the extension-side pressure introductionpassage Ie is closed by the extension-side check valve Te, duringcontraction of the shock absorber D2, the pressure within thecontraction-side back pressure chamber Cp can be increased higher thanthat of the extension-side chamber R1. The pressure of theextension-side back pressure chamber Ce becomes higher than the pressureof the extension-side chamber R1 on the low-pressure side, and biasesthe extension-side second leaf valve Ve2 that closes the extension-sidepassage 3. Since a flow of liquid is not generated in the extension-sidepassage 3, there is no problem even if the extension-side second leafvalve Ve2 closes the extension-side passage 3.

The solenoid pressure control valve 6 is provided in the adjustmentpassage Pc as explained above. When the solenoid Sol of the solenoidpressure control valve 6 is energized so as to control the pressure onthe upstream side of the adjustment passage Pc, the pressure within thecontraction-side back pressure chamber Cp can be adjusted and thecontraction-side load can be controlled to a desired load. Given theabove, the contraction-side load that compresses the contraction-sidesecond leaf valve Vp2 can be controlled by the solenoid pressure controlvalve 6. By controlling the contraction-side load, the gap amount of thecontraction-side first gap between the contraction-side first leaf valveVp1 and the contraction-side valve seat 2 c (the opening degree of thecontraction-side first leaf valve Vp1) in a state in which thecontraction-side first leaf valve Vp1 abuts the contraction-side secondleaf valve Vp2 can be controlled. Thereby, the contraction-side dampingforce during contraction of the shock absorber D2 can be controlled.

Next, a case in which the damping force characteristics of the shockabsorber D2 are set to hard, i.e. a case in which the biasing force thatis generated by the biasing part and biases the extension-side secondleaf valve Ve2 and the contraction-side second leaf valve Vp2 isincreased and the damping coefficient is increased, will be explained.In order to make the damping force characteristics hard, the biasingforce generated by the biasing part is controlled so that theextension-side second leaf valve Ve2 and the contraction-side secondleaf valve Vp2 deflect so as to abut the corresponding extension-sidefirst leaf valve Ve1 and the contraction-side first leaf valve Vp1, andthe extension-side first leaf valve Ve1 and the contraction-side firstleaf valve Vp1 deflect so as to sit on the corresponding extension-sidevalve seat 2 d and the contraction-side valve seat 2 c. The solenoid Solis energized so as to increase the resistance applied by the solenoidpressure control valve 6 to the passing liquid.

In this state, the extension-side second leaf valve Ve2 abuts theextension-side first leaf valve Ve1 and the extension-side first leafvalve Ve1 sits on the extension-side valve seat 2 d, and theextension-side first gap and the extension-side second gap are notformed. Similarly, the contraction-side second leaf valve Vp2 abuts thecontraction-side first leaf valve Vp1 and the contraction-side firstleaf valve Vp1 sits on the contraction-side valve seat 2 c, and thecontraction-side first gap and the contraction-side second gap are notformed.

When the piston 2 moves upward in FIG. 5 at a low piston speed and theshock absorber D2 extends, the gap amount of the extension-side firstgap that is formed between the extension-side first leaf valve Ve1 andthe extension-side valve seat 2 d is very small even if theextension-side first leaf valve Ve1 deflects upon receiving the pressureof the extension-side chamber R1 via the extension-side passage 3. Theliquid passing through the extension-side passage 3 passes through theextension-side first gap consisting of a small gap amount, and thus theshock absorber D2 can exert a larger damping force compared to the casein which the damping characteristics are set to be soft.

On the other hand, if the piston speed is high, the pressure of theextension-side chamber R1 that acts on the extension-side first leafvalve Ve1 via the extension-side passage 3 increases. If the force in adirection causing the extension-side first leaf valve Ve1 to separatefrom the extension-side valve seat 2 d that is generated by the pressureof the extension-side chamber R1 increases, the extension-side firstleaf valve Ve1 and the extension-side second leaf valve Ve2 deflectgreatly, and the extension-side annular plate 268 and the extension-sidespool Se are pushed downward in FIG. 7 . As a result, the gap amount ofthe extension-side first gap between the extension-side first leaf valveVe1 and the extension-side valve seat 2 d increases. Since the biasingforce generated by the biasing part is large compared to the state inwhich the damping force characteristics are set to be soft, the amountof deflection of the extension-side first leaf valve Ve1 is small. Sincethe gap amount of the extension-side first gap is also small, asindicated by the line E2 in FIG. 8 , even at the same piston speed, theshock absorber D2 exerts a higher damping force when set to hard thanwhen set to soft.

Similar to the case in which the damping force characteristics are setto soft, the liquid within the extension-side chamber R1 pushes andopens the extension-side check valve Te and passes through theextension-side pressure introduction chamber Ie to flow into theadjustment passage Pc. By controlling the pressure on the upstream sideof the adjustment passage Pc with the solenoid pressure control valve 6provided to the adjustment passage Pc, similar to when set to soft, thepressure within the extension-side back pressure chamber Ce can beadjusted and the extension-side load can be controlled to a desiredload, and the opening degree of the extension-side first leaf valve Ve1can be controlled. Thereby, the damping force (extension-side dampingforce) during extension of the shock absorber D2 in which the dampingforce characteristics have been set to hard can be controlled.

When the piston 2 moves downward in FIG. 5 at a low piston speed and theshock absorber D2 contracts, the gap amount of the contraction-sidefirst gap that is formed between the contraction-side first leaf valveVp1 and the contraction-side valve seat 2 c is very small even if thecontraction-side first leaf valve Vp1 deflects upon receiving thepressure of the contraction-side chamber R2 via the contraction-sidepassage 4. The liquid passing through the contraction-side passage 4passes through the contraction-side first gap consisting of a small gapamount, and thus the shock absorber D2 can exert a larger damping forcecompared to the case in which the damping characteristics are set to besoft.

On the other hand, if the piston speed is high, the pressure of thecontraction-side chamber R2 that acts on the contraction-side first leafvalve Vp1 via the contraction-side passage 4 increases. If the force ina direction causing the contraction-side first leaf valve Vp1 toseparate from the contraction-side valve seat 2 c that is generated bythe pressure of the contraction-side chamber R2 increases, thecontraction-side first leaf valve Vp1 and the contraction-side secondleaf valve Vp2 deflect greatly, and the contraction-side annular plate263 and the contraction-side spool Sp are pushed upward in FIG. 7 . As aresult, the gap amount of the contraction-side first gap between thecontraction-side first leaf valve Vp1 and the contraction-side valveseat 2 c increases. Since the biasing force generated by the biasingpart is large compared to the state in which the damping forcecharacteristics are set to be soft, the amount of deflection of thecontraction-side first leaf valve Vp1 is small. Since the gap amount ofthe contraction-side first gap is also small, as indicated by the lineF2 in FIG. 8 , even at the same piston speed, the shock absorber D2exerts a higher damping force when set to hard than when set to soft.

Similar to the case in which the damping force characteristics are setto soft, the liquid within the contraction-side chamber R2 pushes andopens the contraction-side check valve Tp and passes through thecontraction-side pressure introduction chamber Ip to flow into theadjustment passage Pc. By controlling the pressure on the upstream sideof the adjustment passage Pc with the solenoid pressure control valve 6provided to the adjustment passage Pc, similar to when set to soft, thepressure within the contraction-side back pressure chamber Cp can beadjusted and the contraction-side load can be controlled to a desiredload, and the opening degree of the contraction-side first leaf valveVp1 can be controlled. Thereby, the damping force (contraction-sidedamping force) during contraction of the shock absorber D2 in which thedamping force characteristics have been set to hard can be controlled.

In this way, in the damping valve and shock absorber D2 of the presentembodiment, the extension-side and contraction-side first gaps areformed between the extension-side and contraction-side first leaf valvesVe1, Vp1 and the corresponding extension-side and contraction-side valveseats 2 d, 2 c. Further, the extension-side and contraction-side secondgaps are formed between the extension-side and contraction-side firstleaf valves Ve1, Vp1 and the corresponding extension-side andcontraction-side second leaf valves Ve2, Vp2. Therefore, when thedamping characteristics are set to soft, compared to a conventionaldamping valve and shock absorber using a fixed orifice, the flow passagearea can be increased and the damping force can be greatly decreasedwhen the piston speed is in a low-speed region. In addition, theextension-side and contraction-side second gaps are formed between theextension-side and contraction-side first leaf valves Ve1, Vp1 and thecorresponding extension-side and contraction-side second leaf valvesVe2, Vp2. Therefore, even if the deflection rigidity of theextension-side and contraction-side first leaf valves Ve1, Vp1 is low,the overall deflection rigidity of the extension-side andcontraction-side first leaf valves Ve1, Vp1 and the correspondingextension-side and contraction-side second leaf valves Ve2, Vp2increases in a state in which the extension-side and contraction-sidefirst leaf valves Ve1, Vp1 deflect and abut the correspondingextension-side and contraction-side second leaf valves Ve2, Vp2. Thus,the damping force can be increased when the piston speed is high, and byreducing the deflection rigidity of the extension-side andcontraction-side first leaf valves Ve1, Vp1, the damping force can befurther decreased when the piston speed is low.

Thus, according to the damping valve and the shock absorber D2 of thepresent embodiment, the damping force when the piston speed is in alow-speed region can be decreased and the damping force adjustment widthcan be expanded.

Further, since the rigidity of the extension-side first leaf valve Ve1can be reduced, during the switch from the extension operation to thecontraction operation of the shock absorber D2, the extension-side firstleaf valve Ve1 can receive the pressure of the contraction-side chamberR2 and quickly sit on the extension-side valve seat 2 d. Also, since therigidity of the contraction-side first leaf valve Vp1 can be reduced,during the switch from the contraction operation to the extensionoperation of the shock absorber D2, the contraction-side first leafvalve Vp1 can receive the pressure of the extension-side chamber R1 andquickly sit on the contraction-side valve seat 2 c. In this way, theextension-side first leaf valve Ve1 and the contraction-side first leafvalve Vp1 can quickly function as check valves without any delays inclosing, and thus the damping force generation responsiveness can beimproved.

In the case that the damping force characteristics of the shock absorberD2 according to the present embodiment are switched from soft to hardduring the extension operation, the extension-side first gap between theextension-side first leaf valve Ve1 and the extension-side valve seat 2d gradually decreases due to the increase in pressure within theextension-side back pressure chamber Ce, and thus the extension-sidefirst leaf valve Ve1 sits on the extension-side valve seat 2 d. In thecase that the damping force characteristics of the shock absorber D2 areswitched from soft to hard during the contraction operation, thecontraction-side first gap between the contraction-side first leaf valveVp1 and the contraction-side valve seat 2 c gradually decreases due tothe increase in pressure within the contraction-side back pressurechamber Cp, and thus the contraction-side first leaf valve Vp1 sits onthe contraction-side valve seat 2 c. Conversely, in the case that thedamping force characteristics of the shock absorber D2 according to thepresent embodiment are switched from hard to soft during the extensionoperation, the extension-side first gap between the extension-side firstleaf valve Ve1 and the extension-side valve seat 2 d gradually increasesdue to the decrease in pressure within the extension-side back pressurechamber Ce. In the case that the damping force characteristics of theshock absorber D2 according to the present embodiment are switched fromhard to soft during the contraction operation, the contraction-sidefirst gap between the contraction-side first leaf valve Vp1 and thecontraction-side valve seat 2 c gradually increases due to the decreasein pressure within the contraction-side back pressure chamber Cp.Therefore, when the damping force characteristics of the shock absorberD2 are switched from soft to hard or from hard to soft, any suddenchanges in the damping force characteristics of the shock absorber D2are mitigated. In a vehicle equipped with the shock absorber D2, suddenchanges in the damping force characteristics are mitigated, and thusshocks during switching of the damping force characteristics are notperceived by the passengers, and the riding comfort of the vehicle canbe improved.

When the solenoid pressure control valve 6 provided to the adjustmentpassage Pc has closed due to a switch in the damping characteristicsfrom soft to hard or the like, the pressures of the extension-side backpressure chamber Ce and the contraction-side back pressure chamber Cpinstantaneously rise, i.e. a so-called surge occurs. In related dampingvalves, if a pressure fluctuation of a back pressure chamber that biasesa leaf valve occurs, the biasing force that biases a disc valve changessuddenly and thus the damping force also changes quickly, and this maynegatively impact the riding comfort in the vehicle.

In the present embodiment, since the extension-side and contraction-sidesecond gaps are provided between the extension-side and contraction-sidefirst leaf valves Ve1, Vp1 and the corresponding extension-side andcontraction-side second leaf valves Ve2, Vp2, the extension-side andcontraction-side second leaf valves Ve2, Vp2 cannot suddenly abut thecorresponding extension-side and contraction-side first leaf valves Ve1,Vp1. Therefore, the extension-side and contraction-side first leafvalves Ve1, Vp1 are not suddenly pushed into the correspondingextension-side valve seat 2 d and contraction-side valve seat 2 c, andthus there are no sudden closures of the extension-side passage 3 andthe contraction-side passage 4. Accordingly, spikes caused by suddenchanges in the damping force do not occur in the damping force waveform,and the riding comfort in the vehicle is not negatively impacted.

The extension-side annular plate 268 is laminated on the back surface ofthe extension-side second leaf valve Ve2, and the extension-side annularplate 268 is slidingly mounted on the outer periphery of theextension-side spacer 267. The contraction-side annular plate 263 islaminated on the back surface of the contraction-side second leaf valveVp2, and the contraction-side annular plate 263 is slidingly mounted onthe outer periphery of the contraction-side spacer 262. Therefore, bysetting the rigidity of the extension-side annular plate 268 to behigher than the rigidity of the extension-side second leaf valve Ve2 andsetting the rigidity of the contraction-side annular plate 263 to behigher than the rigidity of the contraction-side second leaf valve Vp2,the biasing force generated by the biasing part can be received by theextension-side annular plate 268 and the contraction-side annular plate263. Thus, deformation of the extension-side first and second leafvalves Ve1, Ve2 and the contraction-side first and second leaf valveVp1, Vp2 can be suppressed, and deterioration of the leaf valves Ve1,Ve2, Vp1, Vp2 can be suppressed.

The extension-side annular plate 268 is slidingly mounted on the outerperiphery of the extension-side spacer 267 that is laminated on the backsurface of the extension-side second leaf valve Ve2, and thecontraction-side annular plate 263 is slidingly mounted on the outerperiphery of the contraction-side spacer 262 that is laminated on theback surface of the contraction-side second leaf valve Vp2. The innerdiameter of the extension-side annular plate 268 is smaller than theouter diameter of the inner peripheral seat part 2 h of the piston 2,and the outer diameter of the extension-side annular plate 268 isgreater than the inner diameter of the extension-side valve seat 2 d.Further, the inner diameter of the contraction-side annular plate 263 issmaller than the outer diameter of the inner peripheral seat part 2 f ofthe piston 2, and the outer diameter of the contraction-side annularplate 263 is greater than the inner diameter of the contraction-sidevalve seat 2 c. Therefore, the pressure on the back surfaces of theextension-side second leaf valve Ve2 and the contraction-side secondleaf valve Vp2 can be received by the extension-side annular plate 268and the contraction-side annular plate 263. Accordingly, by providingthe extension-side annular plate 268 and the contraction-side annularplate 263 to the shock absorber D2, excessive loads on theextension-side first and second leaf valves Ve1, Ve2 and thecontraction-side first and second leaf valves Vp1, Vp2 can be prevented,and the rigidity of the extension-side first leaf valve Ve1 and thecontraction-side first leaf valve Vp2 can be further reduced, and thusleaf valves with lower deflection rigidity can be utilized. Therefore, alower damping force can be exerted by the shock absorber D2.

Further, the biasing part biases the extension-side second leaf valveVe2 and the contraction-side second leaf valve Vp2 using either one orboth of the pressures of the extension-side chamber R1 and thecontraction-side chamber R2 within the shock absorber D2. Therefore, theextension-side second leaf valve Ve2 and the contraction-side secondleaf valve Vp2 can be biased without using a biasing force generationsource, and the biasing force can be changed by controlling thepressure.

In general, in a shock absorber for a vehicle, in order to suppressvibrations in the up-down direction of the vehicle body, it is necessaryto make the extension-side damping force during the extension operationgreater than the contraction-side damping force during the contractionoperation. In the shock absorber D2 that is set to a single-rod type,the pressure-receiving area that receives the pressure of theextension-side chamber R1 is an area obtained by subtracting thecross-section area of the rod member 10 from the cross-section area ofthe piston 2. Thus, it is necessary to make the pressure of theextension-side chamber R1 during the extension operation much greaterthan the pressure of the contraction-side chamber R2 during thecontraction operation.

In contrast, in the shock absorber D2 according to the presentembodiment, in the case that the extension-side back pressure chamber Ceand the contraction-side back pressure chamber Cp are at equalpressures, the extension-side load that biases the extension-side firstleaf valve Ve1 is greater than the contraction-side load that biases thecontraction-side first leaf valve Vp1. Further, in the presentembodiment, the extension-side spool Se is used. Compared to a structurein which the extension-side spool Se is not used and the pressure of theextension-side back pressure chamber Ce is merely made to act on theback surface side of the extension-side second leaf valve Ve2, thepressure-receiving area of the extension-side spool Se that receives thepressure of the extension-side back pressure chamber Ce can be madegreater than the back surface area of the extension-side second leafvalve Ve2. Therefore, a large extension-side load can be made to act onthe extension-side second leaf valve Ve2. Further, by using theextension-side spool Se and the contraction-side spool Sp, the degree offreedom for designing the extension-side load and the contraction-sideload can be improved.

Accordingly, in the shock absorber D2 of the present embodiment, in thecase that it is necessary to greatly increase the extension-side load inorder to adjust the extension-side damping force during the extensionoperation, it is possible to make settings so as to output a largeextension-side load even if the pressure of the extension-side backpressure chamber Ce is small. Thus, the control width of theextension-side damping force can be secured even without using a largesolenoid Sol.

Instead of performing pressure control of the extension-side backpressure chamber Ce and the contraction-side back pressure chamber Cp bydriving independent valve bodies, by making the extension-side loadgreater than the contraction-side load, the control width of theextension-side damping force can be secured even if the pressures of theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp are controlled in communication with each other.Thus, it is sufficient to provide a single valve body 31 of the solenoidvalve to the solenoid pressure control valve 6. Therefore, the structurebecomes extremely simple and the costs can also be lowered.

Due to the above, the size of the solenoid Sol in the solenoid pressurecontrol valve 6 can be decreased, and in addition, the structure of thesolenoid pressure control valve 6 is simplified and the size of theshock absorber D2 does not increase even if the solenoid pressurecontrol valve 6 is utilized in the piston part of the shock absorber D2.Thus, according to the shock absorber D2 of the present embodiment, thestructure of the shock absorber D2 is simplified and the size thereof isreduced, and the installation into the vehicle is not negativelyaffected. Further, since the extension-side damping force can beincreased even if the solenoid Sol does not exert a large thrust, thepower consumption when increasing the damping force can be reduced andthus power saving can be achieved.

Since the pressure-receiving area of the extension-side spool Se thatreceives the pressure of the extension-side back pressure chamber Ce isconfigured to be greater than the pressure-receiving area of thecontraction-side spool Sp that receives the pressure of thecontraction-side back pressure chamber Cp, the extension-side load canbe easily configured to be greater than the contraction-side load.

The extension-side back pressure chamber Ce and the contraction-sideback pressure chamber Cp communicate with each other through thecommunication passage 24 via the contraction-side resistance element andthe extension-side resistance element. The contraction-side pressureintroduction passage Ip introduces liquid from the contraction-sidechamber R2 to the extension-side back pressure chamber Ce with hardlyany resistance. Therefore, when the shock absorber D2 switches from theextension operation to the contraction operation, the pressure withinthe contraction-side chamber R2 is quickly introduced into theextension-side back pressure chamber Ce. Thus, the extension-side spoolSe presses the extension-side second leaf valve Ve2 by means of thepressure within the extension-side back pressure chamber Ce and thebiasing by the spring member 16 so that the extension-side first leafvalve Ve1 can be quickly seated on the extension-side valve seat 2 d toclose the extension-side passage 3. The extension-side pressureintroduction passage Ie also introduces liquid from the extension-sidechamber R1 to the contraction-side back pressure chamber Cp with hardlyany resistance. Therefore, when the shock absorber D2 switches from thecontraction operation to the extension operation, the pressure withinthe extension-side chamber R1 is quickly introduced into thecontraction-side back pressure chamber Cp. Thus, the contraction-sidespool Sp presses the contraction-side second leaf valve Vp2 by means ofthe pressure within the contraction-side back pressure chamber Cp andthe biasing by the spring member 20 so that the contraction-side firstleaf valve Vp1 can be quickly seated on the contraction-side valve seat2 c to close the contraction-side passage 4.

Gaps may form between the annular plate 19 and the contraction-sidechamber 11 and between the annular plate 15 and the extension-sidechamber 12 due to deterioration over time of the valve body (annularplate 19) of the extension-side check valve Te and the valve body(annular plate 15) of the contraction-side check valve Tp. Since theextension-side resistance element and the contraction-side resistanceelement are not provided to the extension-side pressure introductionpassage Ie and the contraction-side pressure introduction passage Ip,the flow amounts passing through the extension-side pressureintroduction passage Ie and the contraction-side pressure introductionpassage Ip do not change. Therefore, the above-mentioned gaps do notaffect the damping force control or the valve-closing operation duringswitching between extension/contraction.

On the outer peripheral side of the piston rod 7, the piston 2, theextension-side first leaf valve Ve1, the extension-side second leafvalve Ve2, the contraction-side first leaf valve Vp1, thecontraction-side second leaf valve Vp2, the cylindrical extension-sidechamber 12, and the cylindrical contraction-side chamber 11 are mounted.The piston 2 includes the extension-side passage 3 and thecontraction-side passage 4, and the extension-side first leaf valve Ve1,the extension-side second leaf valve Ve2, the contraction-side firstleaf valve Vp1, and the contraction-side second leaf valve Vp2 arelaminated on the piston 2. The extension-side chamber 12 forms theextension-side back pressure chamber Ce, and the extension-side spool Seis slidingly inserted into the inner periphery of the extension-sidechamber 12. The contraction-side chamber 11 forms the contraction-sideback pressure chamber Cp, and the contraction-side spool Sp is slidinglyinserted into the inner periphery of the contraction-side chamber 11.The contraction-side pressure introduction passage Ip is provided to theextension-side chamber 12, and the extension-side pressure introductionpassage Ie is provided to the contraction-side chamber 11, and thus themembers required to adjust the damping force can be disposed in aconcentrated manner in the piston part of the shock absorber D2.

The extension-side second leaf valve Ve2 of the extension-side spool Seand the valve body (annular plate 15) of the contraction-side checkvalve Tp that opens/closes the contraction-side pressure introductionpassage Ip are biased by the single spring member 16. Thecontraction-side second leaf valve Vp2 of the contraction-side spool Spand the valve body (annular plate 19) of the extension-side check valveTe that opens/closes the extension-side pressure introduction passage Ieare biased by the single spring member 20. Therefore, the check valvesTe, Tp and the spools Se, Sp can be restored to the return side with thesingle spring members 16, 20, and thus the number of parts can bereduced.

In the shock absorber D2, the retaining shaft 8 a, the vertical hole 8d, the extension-side pilot orifice Pe serving as the extension-sideresistance element, the contraction-side pilot orifice Pp serving as thecontraction-side resistance element, the accommodation part L, theadjustment passage Pc, and the contraction-side discharge passage Ep areprovided to the piston rod 7. The retaining shaft 8 a is provided on thedistal end of the piston rod 7, and the piston 2, the extension-sidefirst leaf valve Ve1, the extension-side second leaf valve Ve2, thecontraction-side first leaf valve Vp1, the contraction-side second leafvalve Vp2, the extension-side chamber 12, and the contraction-sidechamber 11 are mounted on the outer periphery of the retaining shaft 8a. The vertical hole 8 d opens from the distal end of the retainingshaft 8 a. The extension-side pilot orifice Pe and the contraction-sidepilot orifice Pp are provided to the retaining shaft 8 a, andcommunicate with the communication passage 24 provided in the verticalhole 8 d. The accommodation part L is provided on the inside of thepiston rod 7 so as to communicate with the vertical hole 8 d, and thesolenoid pressure control valve 6 is accommodated in the accommodationpart L. The adjustment passage Pc allows the communication passage 24 tocommunicate with the accommodation part L. The contraction-sidedischarge passage Ep allows the accommodation part L to communicate withthe extension-side chamber R1. The shock absorber D2 includes theseparator 23 that is inserted into the vertical hole 8 d. The separator23 forms, by the annular groove 23 a provided on the outer peripherythereof, the communication passage 24 that allows the extension-sideback pressure chamber Ce to communicate with the contraction-side backpressure chamber Cp within the vertical hole 8 d. The separator 23 alsoforms the extension-side discharge passage Ee on the inner peripherythereof. Therefore, the solenoid pressure control valve 6 can beaccommodated within the piston rod 7 without any trouble, and theextension-side back pressure chamber Ce and the contraction-side backpressure chamber Cp can be provided on the outer periphery of the pistonrod 7 shifted in the axial direction from the solenoid pressure controlvalve 6.

Similar to the first embodiment, the shock absorber D2 can stabilize thevehicle body posture even during a failure. By making the solenoidpressure control valve 6 function as a throttle valve, the ridingcomfort in the vehicle can be improved even during a failure.

Similar to the first embodiment, the solenoid pressure control valve 6blocks the adjustment passage Pc by making the small-diameter part 31 aoppose the through hole 30 c. Therefore, the pressure-receiving area onwhich pressure in a direction in which the valve body 31 of the solenoidvalve escapes from the valve seat member 30 acts can be greatlydecreased, and thus the flow passage area during valve opening can beincreased. Accordingly, the movement of the valve body 31 of thesolenoid valve is stable. Further, in the blocked position, the solenoidpressure control valve remains closed even upon receiving pressure fromthe upstream side, and thus it is possible to activate only the failvalve FV.

The constitution of the biasing part is not limited to that in thepresent embodiment. The present embodiment can also be applied to onlyeither one of the damping valve on the extension-side or the dampingvalve on the contraction-side of the shock absorber. Although notillustrated, the present embodiment can also be applied to a dampingvalve provided to a base valve instead of a damping valve provided tothe piston part of a shock absorber.

Embodiments of this invention were described above, but the aboveembodiments are merely examples of applications of this invention, andthe technical scope of this invention is not limited to the specificconstitutions of the above embodiments.

This application claims priority based on Japanese Patent ApplicationNo. 2014-237842 filed with the Japan Patent Office on Nov. 25, 2014, andJapanese Patent Application No. 2014-237846 filed with the Japan PatentOffice on Nov. 25, 2014, the entire contents of which are incorporatedby reference into this specification.

The invention claimed is:
 1. A damping valve, comprising: a valve discincluding at least one passage and a valve seat provided to surround anoutlet end of the at least one passage; a first annular leaf valvedisposed on the valve disc spaced from the valve seat in an axialdirection of the valve disc in a state in which a load does not act onthe first annular leaf valve, the first annular leaf valve beingconfigured to sit on the valve seat by deflection of an outer peripheryof the first annular leaf valve toward the valve seat so as to close theat least one passage, the first annular leaf valve being configured toseparate from the valve seat by termination of the deflection so as toopen the at least one passage; a second annular leaf valve disposed on aside of the first annular leaf valve opposite to a side of the firstannular leaf valve at which the valve disc is disposed, the secondannular leaf valve being spaced from the first annular leaf valve in theaxial direction, the second annular leaf valve being configured to causethe outer periphery of the first annular leaf valve to deflect bydeflection of an outer periphery of the second annular leaf valve towardthe valve seat; a biasing part configured to exert a variable biasingforce on the second annular leaf valve to cause the outer periphery ofthe second annular leaf valve to deflect toward the valve seat; a spacerlaminated on a side of the second annular leaf valve opposite to a sideof the second annular leaf valve at which the valve disc is disposed,the spacer having an outer diameter smaller than that of the secondannular leaf valve; and an annular plate mounted on an outer peripheryof the spacer slidably in the axial direction, wherein the biasing partis configured to slide the annular plate on the outer periphery of thespacer toward the valve disc to cause the outer periphery of the secondannular leaf valve to deflect toward the valve seat.
 2. The dampingvalve according to claim 1, wherein the biasing part is configured tocause the second annular leaf valve to abut and compress the firstannular leaf valve so as to make the first annular leaf valve sit on thevalve seat.
 3. The damping valve according to claim 1, wherein the valvedisc further includes an inner seat part radially inside the at leastone passage, the inner seat part being configured to support an innerpart of the first annular leaf valve, an inner diameter of the annularplate is smaller than an outer diameter of the inner seat part, and anouter diameter of the annular plate is greater than an inner diameter ofthe valve seat.
 4. A shock absorber, comprising: a cylinder; the dampingvalve according to claim 1 and accommodated within the cylinder; anextension-side chamber and a contraction-side chamber partitioned withinthe cylinder by the valve disc; and a piston rod movably inserted intothe cylinder and connected to the valve disc, wherein the extension-sidechamber and the contraction-side chamber communicate with each otherthrough the at least one passage.
 5. The shock absorber according toclaim 4, wherein: the at least one passage comprises an extension-sidepassage and a contraction-side passage, each of the extension-sidepassage and the contraction-side passage being configured to allow theextension-side chamber to communicate with the contraction-side chamber;the valve seat comprises an extension-side valve seat and acontraction-side valve seat, the extension-side valve seat beingprovided to surround the outlet end of the extension-side passage, thecontraction-side valve seat being provided to surround the outlet end ofthe contraction-side passage; the first annular leaf valve comprises anextension-side first leaf valve configured to open and close theextension-side passage, and a contraction-side first leaf valveconfigured to open and close the contraction-side passage; and thesecond annular leaf valve comprises an extension-side second leaf valvedisposed on a side of the extension-side first leaf valve opposite to aside of the extension-side first leaf valve at which the valve disc isdisposed, and a contraction-side second leaf valve disposed on a side ofthe contraction-side first leaf valve opposite to a side of thecontraction-side first leaf valve at which the valve disc is disposed,the biasing part comprises: an extension-side spool configured to biasthe extension-side second leaf valve utilizing pressure of theextension-side chamber; an extension-side back pressure chamberconfigured to press the extension-side spool with internal pressure; acontraction-side spool configured to bias the contraction-side secondleaf valve utilizing pressure of the contraction-side chamber; acontraction-side back pressure chamber configured to press thecontraction-side spool with internal pressure; a communication passageconfigured to communicate with the contraction-side back pressurechamber via an extension-side resistance element configured to applyresistance to a flow of passing liquid, and configured to communicatewith the extension-side back pressure chamber via a contraction-sideresistance element configured to apply resistance to a flow of passingliquid; an extension-side pressure introduction passage configured topermit a flow of liquid in only one direction from the extension-sidechamber toward the contraction-side back pressure chamber; acontraction-side pressure introduction passage configured to permit aflow of liquid in only one direction from the contraction-side chambertoward the extension-side back pressure chamber; an adjustment passageconnected to the communication passage; a contraction-side dischargepassage configured to allow a downstream of the adjustment passage tocommunicate with the extension-side chamber, and configured to permit aflow of liquid in only one direction from the adjustment passage towardthe extension-side chamber; an extension-side discharge passageconfigured to allow a downstream of the adjustment passage tocommunicate with the contraction-side chamber, and configured to permita flow of liquid in only one direction from the adjustment passagetoward the contraction-side chamber; and a solenoid pressure controlvalve provided in the adjustment passage and configured to controlupstream pressure of the adjustment passage.
 6. The shock absorberaccording to claim 5, wherein when the pressure of the extension-sideback pressure chamber and the pressure of the contraction-side backpressure chamber are the same, an extension-side load biasing theextension-side second leaf valve by the pressure of the extension-sideback pressure chamber is greater than a contraction-side load biasingthe contraction-side second leaf valve by the pressure of thecontraction-side back pressure chamber.
 7. The shock absorber accordingto claim 6, wherein a pressure-receiving area of the extension-sidespool configured to receive the pressure of the extension-side backpressure chamber is greater than a pressure-receiving area of thecontraction-side spool configured to receive the pressure of thecontraction-side back pressure chamber.
 8. A damping valve, comprising:a valve disc including at least one passage and a valve seat provided tosurround an outlet end of the at least one passage; a first annular leafvalve disposed on the valve disc spaced from the valve seat in an axialdirection of the valve disc in a state in which a load does not act onthe first annular leaf valve, the first annular leaf valve beingconfigured to sit on the valve seat by deflection of an outer peripheryof the first annular leaf valve toward the valve seat so as to close theat least one passage, the first annular leaf valve being configured toseparate from the valve seat by termination of the deflection so as toopen the at least one passage; a second annular leaf valve disposed on aside of the first annular leaf valve opposite to a side of the firstannular leaf valve at which the valve disc is disposed, the secondannular leaf valve being spaced from the first annular leaf valve in theaxial direction, the second annular leaf valve being configured to causethe outer periphery of the first annular leaf valve to deflect bydeflection of an outer periphery of the second annular leaf valve towardthe valve seat; a biasing part configured to exert a variable biasingforce on the second annular leaf valve to cause the outer periphery ofthe second annular leaf valve to deflect toward the valve seat; at leastone first annular spacer interposed between the first annular leaf valveand the valve disc, the at least one first annular spacer beingconfigured to adjust a gap between the first annular leaf valve and thevalve seat; and at least one second annular spacer interposed betweenthe second annular leaf valve and the first annular leaf valve, the atleast one second annular spacer being configured to adjust a gap betweenthe second annular leaf valve and the first annular leaf valve.